WO2009095817A1

WO2009095817A1 - Lighting unit and thermal management system and method therefor

Info

Publication number: WO2009095817A1
Application number: PCT/IB2009/050225
Authority: WO
Inventors: Ian Edward Ashdown
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-01-31
Filing date: 2009-01-21
Publication date: 2009-08-06
Also published as: TW200942075A

Abstract

Disclosed is a thermal management system for a lighting unit (1000) including a light source (1004), wherein the thermal management system includes a converting element (1020) configured and disposed to absorb at least some of the light generated by the light source (1004) and emit converted light in response thereto, wherein the intensity of the converted light decays in accordance with a temperature dependent characteristic of said converting element (1020). The system further includes a sensing element (1006) configured to sense a first intensity of the converted light, and one or more subsequent decreased intensities thereof during an off-state of said light source (1004). The system is configured to determine, based at least in part on first intensity and the one or more subsequent intensities, a value indicative of an operating temperature of the light source (1004).

Description

LIGHTING UNIT AND THERMAL MANAGEMENT SYSTEM AND METHOD THEREFOR

Technical Field

[0001] The present invention is directed generally to lighting units. More particularly, various inventive methods and apparatus disclosed herein relate to temperature measurement and/or management for a light source.

Background

[0002] Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Patent Nos. 6,016,038 and 6,211,626.

[0003] Advances in the development and improvements of the luminous flux of light- emitting devices such as solid-state semiconductor and organic LEDs have made these devices suitable for use in general illumination applications, including architectural, entertainment, and roadway lighting. Light-emitting diodes are becoming increasingly competitive with light sources such as incandescent, fluorescent, and high-intensity discharge lamps.

[0004] In general, these lighting units comprise one or more LEDs or LED packages each comprising a substrate to which one or more LEDs are mounted. As the ambient temperature changes, or as the power at which the LEDs are driven changes, the temperature of the LEDs may also change. Such changes in LED temperature may lead to wavelength shifts, luminous flux output variations and other such generally undesirable effects. In white light or color changing LED light sources, these wavelength shifts and luminous flux output changes, which may be different for LEDs of a same or different lot, may affect the color temperature and/or output intensity of the light source. Furthermore, when driving LEDs at high currents {e.g., high intensity LEDs), for instance to maximize an output of the lighting unit, the LED temperature may rise significantly, which may lead to a reduction in LED lifetime and/or operating efficiency. Accordingly, effective monitoring and/or controlling temperature changes in LED lighting units is desirable.

[0005] Some known methods of measuring the junction temperature of a light-emitting diode include measuring LED package temperature and/or LED forward voltage. With one such method, a thermistor is mounted close to and in good thermal contact with the LED package. If the thermal resistance between the LED junction and the thermistor is known or can be estimated, the LED junction temperature can be determined. This method, however, can be limited by the thermal capacity of the LED package and thermal management system, typically comprising a passive heat sink or heat pipe. With this measuring technique, sudden changes in the LED junction temperature due to changes in the LED drive current cannot be measured at a rate faster than the thermal time constant between the LED junction and the thermistor.

[0006] In another method, the forward voltage across the LED junction and electrical leads is determined in part by the circuit resistance. When the LED is operated in the linear region of its current-voltage (I-V) characteristic curve, a change in forward voltage is due to Joule heating, and so is linearly proportional to the corresponding change in LED junction temperature. This method however is limited by the low circuit resistance of high-intensity LEDs, which results in small changes in forward voltage. As a result, it may be difficult to accurately measure the absolute voltages in the presence of electrical switching noise from the LED drivers, thereby resulting in a difficulty of accurately evaluating LED junction temperature.

[0007] Thus, there is a need in the art for a lighting unit and thermal management system and method therefor capable of determining and/or managing the temperature of a light source with a desired rate of data acquisition and/or accuracy. Summary

[0008] This disclosure is directed to inventive methods and apparatus for temperature measurement and/or management for a light source. In its various embodiments, the present invention relates to an apparatus and method for the measurement of LED junction temperature in a manner that provides the desired rate of data acquisition and/or accuracy.

[0009] Generally, in one aspect, the present invention focuses on a thermal management system for a lighting unit including a light source configured to generate light. The system further includes a converting element configured and disposed to absorb at least some of the light generated by the light source and emit converted light in response thereto, an intensity of said converted light decaying in accordance with a temperature dependent characteristic of said converting element; and a sensing element configured to sense a first intensity of said converted light, and one or more subsequent decreased intensities thereof during an off-state of said light source. The system is configured to determine, based at least in partially on said first intensity and said one or more subsequent intensities, a value indicative of an operating temperature of the light source. The converting element may include a phosphor material, quantum dot material or a luminescent dopant material.

[0010] In accordance with another aspect of the invention, there is provided a lighting unit including: a light source configured to emit light; a converting element configured and disposed to absorb at least some of the light generated by said light source and emit converted light in response thereto, an intensity of said converted light decaying in accordance with a temperature dependent characteristic of said converting element; a sensing element configured to sense a first intensity of said converted light, and one or more subsequent decreased intensities thereof during an off-state of said light source; and a thermal management module operatively coupled to said sensing element and configured to determine, from said first intensity and said one or more subsequent intensities, a value indicative of an operating temperature of said light source.

[0011] In one embodiment of the invention, the thermal management module is further configured to adjust an operational characteristic of the lighting unit in response to said value. [0012] In accordance with yet another aspect of the invention, there is provided a method for managing operating temperature of a lighting unit including a light source configured to emit light. The method contemplates the steps of: converting at least some of the light generated by the light source via a converting element having a temperature dependent characteristic; sensing a first intensity of said converted light during an on state of the light source; sensing one or more subsequent intensities of said converted light during an off state of the light source; and determining a value indicative of an operating temperature of the light source from said first intensity and said one or more subsequent intensities based on said temperature dependent characteristic. In accordance with one embodiment of the invention, the method further includes the step of adjusting an operational characteristic of the lighting unit in response to said value.

[0013] As used herein for purposes of the present disclosure, the term "LED" should be understood to include any electroluminescent diode or other type of carrier injection/junction- based system that is capable of generating radiation in response to an electric signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It also should be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.

[0014] For example, one implementation of an LED configured to generate essentially white light (e.g., a white LED) may include a number of dies which respectively emit different spectra of electroluminescence that, in combination, mix to form essentially white light. In another implementation, a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum. In one example of this implementation, electroluminescence having a relatively short wavelength and narrow bandwidth spectrum "pumps" the phosphor material, which in turn radiates longer wavelength radiation having a somewhat broader spectrum.

[0015] It should also be understood that the term LED does not limit the physical and/or electrical package type of an LED. For example, as discussed above, an LED may refer to a single light emitting device having multiple dies that are configured to respectively emit different spectra of radiation (e.g., that may or may not be individually controllable). Also, an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount LEDs, radial package LEDs, power package LEDs, LEDs including some type of encasement and/or optical element (e.g., a diffusing lens), etc.

[0016] The term "light source" should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED-based sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro-luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano-luminescent sources, crystallo- luminescent sources, kine-luminescent sources, thermo-luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.

[0017] A given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both. Hence, the terms "light" and "radiation" are used interchangeably herein. Additionally, a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components. Also, it should be understood that light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination. An "illumination source" is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space. In this context, "sufficient intensity" refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit "lumens" often is employed to represent the total light output from a light source in all directions, in terms of radiant power or "luminous flux") to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part).

[0018] The term "spectrum" should be understood to refer to any one or more frequencies (or wavelengths) of radiation produced by one or more light sources. Accordingly, the term "spectrum" refers to frequencies (or wavelengths) not only in the visible range, but also frequencies (or wavelengths) in the infrared, ultraviolet, and other areas of the overall electromagnetic spectrum. Also, a given spectrum may have a relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or wavelength components) or a relatively wide bandwidth (several frequency or wavelength components having various relative strengths). It should also be appreciated that a given spectrum may be the result of a mixing of two or more other spectra (e.g., mixing radiation respectively emitted from multiple light sources).

[0019] For purposes of this disclosure, the term "color" is used interchangeably with the term "spectrum." However, the term "color" generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms "different colors" implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term "color" may be used in connection with both white and non-white light.

[0020] The term "color temperature" generally is used herein in connection with white light, although this usage is not intended to limit the scope of this term. Color temperature essentially refers to a particular color content or shade (e.g., reddish, bluish) of white light. The color temperature of a given radiation sample conventionally is characterized according to the temperature in degrees Kelvin (K) of a black body radiator that radiates essentially the same spectrum as the radiation sample in question. Black body radiator color temperatures generally fall within a range of from approximately 700 degrees K (typically considered the first visible to the human eye) to over 10,000 degrees K; white light generally is perceived at color temperatures above 1500-2000 degrees K.

[0021] Lower color temperatures generally indicate white light having a more significant red component or a "warmer feel," while higher color temperatures generally indicate white light having a more significant blue component or a "cooler feel." By way of example, fire has a color temperature of approximately 1,800 degrees K, a conventional incandescent bulb has a color temperature of approximately 2848 degrees K, early morning daylight has a color temperature of approximately 3,000 degrees K, and overcast midday skies have a color temperature of approximately 10,000 degrees K. A color image viewed under white light having a color temperature of approximately 3,000 degree K has a relatively reddish tone, whereas the same color image viewed under white light having a color temperature of approximately 10,000 degrees K has a relatively bluish tone.

[0022] The term "lighting fixture" is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package. The term "lighting unit" is used herein to refer to an apparatus including one or more light sources of same or different types. A given lighting unit may have any one of a variety of mounting arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry) relating to the operation of the light source(s). An "LED-based lighting unit" refers to a lighting unit that includes one or more LED- based light sources as discussed above, alone or in combination with other non LED-based light sources. A "multi-channel" lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a "channel" of the multi-channel lighting unit. [0023] The term "controller" is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0024] In various implementations, a processor or controller may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tape, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present invention discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers.

[0025] The term "addressable" is used herein to refer to a device (e.g., a light source in general, a lighting unit or fixture, a controller or processor associated with one or more light sources or lighting units, other non-lighting related devices, etc.) that is configured to receive information (e.g., data) intended for multiple devices, including itself, and to selectively respond to particular information intended for it. The term "addressable" often is used in connection with a networked environment (or a "network," discussed further below), in which multiple devices are coupled together via some communications medium or media.

[0026] In one network implementation, one or more devices coupled to a network may serve as a controller for one or more other devices coupled to the network (e.g., in a master/slave relationship). In another implementation, a networked environment may include one or more dedicated controllers that are configured to control one or more of the devices coupled to the network. Generally, multiple devices coupled to the network each may have access to data that is present on the communications medium or media; however, a given device may be "addressable" in that it is configured to selectively exchange data with (i.e., receive data from and/or transmit data to) the network, based, for example, on one or more particular identifiers (e.g., "addresses") assigned to it.

[0027] The term "network" as used herein refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g. for device control, data storage, data exchange, etc.) between any two or more devices and/or among multiple devices coupled to the network. As should be readily appreciated, various implementations of networks suitable for interconnecting multiple devices may include any of a variety of network topologies and employ any of a variety of communication protocols. Additionally, in various networks according to the present disclosure, any one connection between two devices may represent a dedicated connection between the two systems, or alternatively a non-dedicated connection. In addition to carrying information intended for the two devices, such a non-dedicated connection may carry information not necessarily intended for either of the two devices (e.g., an open network connection). Furthermore, it should be readily appreciated that various networks of devices as discussed herein may employ one or more wireless, wire/cable, and/or fiber optic links to facilitate information transport throughout the network.

[0028] The term "user interface" as used herein refers to an interface between a human user or operator and one or more devices that enables communication between the user and the device(s). Examples of user interfaces that may be employed in various implementations of the present disclosure include, but are not limited to, switches, potentiometers, buttons, dials, sliders, a mouse, keyboard, keypad, various types of game controllers (e.g., joysticks), track balls, display screens, various types of graphical user interfaces (GUIs), touch screens, microphones and other types of sensors that may receive some form of human-generated stimulus and generate a signal in response thereto.

[0029] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

Brief Description of the Drawings

[0030] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

[0031] FIG. 1 illustrates a lighting unit comprising a thermal management system in accordance with an embodiment of the present invention.

[0032] FIG. 2 illustrates a lighting unit comprising a thermal management system in accordance with another embodiment of the present invention.

[0033] FIG. 3 illustrates a lighting unit comprising a thermal management system in accordance with another embodiment of the present invention.

[0034] FIG. 4 illustrates a lighting unit comprising a thermal management system in accordance with another embodiment of the present invention.

[0035] FIG. 5 illustrates a lighting unit comprising a thermal management system in accordance with another embodiment of the present invention. [0036] FIG. 6 illustrates a graphical representation of intensity readings taken during a single on/off cycle of a lighting unit's light source, in accordance with one embodiment of the present invention.

[0037] FIG. 7 illustrates a graphical representation of intensity readings taken during plural on/off cycles of a lighting unit's light source, in accordance with one embodiment of the present invention.

Detailed Description

[0038] Applicants have recognized and appreciated that it would be beneficial to be able to determine and/or manage the temperature of a light source at the desired rate of data acquisition and/or accuracy. In view of the foregoing, various embodiments and implementations of the present invention are directed to a lighting unit, and a thermal management system and method therefor. In general, the lighting units described herein, in accordance with different embodiments of the invention, include one or more light sources and one or more converting elements configured to convert at least some of the light emitted by the one or more light sources and emit converted light in accordance with a temperature dependent characteristic of the converting element(s) (e.g. a temporal temperature-dependent converted light intensity function, etc.). The lighting unit(s) further include one or more sensing elements for sensing temporally distinct intensities of the converted light, and a thermal management module operatively coupled thereto and configured to determine, from the sensed converted light intensities, a value indicative of the operating temperature of the one or more light sources based on the temperature dependent characteristic of the converting element. Optionally, in accordance with some embodiments, the lighting unit may be further adapted to adjust one or more operational characteristics of the lighting unit in response to the determined value(s), for example via the thermal management module, or another module integral thereto or distinct therefrom.

[0039] In some embodiments, the operating temperature of the lighting unit's light source(s) may be monitored to avoid operating the light sources(s) at a temperature that may lead to noticeable and/or significant damage, and/or cause undesirable output fluctuations, variations and/or changes. For example, as the ambient temperature changes, or as the power at which a light source is driven changes, the temperature of the light source may also change. Such changes may raise the operating temperature above an acceptable threshold, at which point the operating conditions of the light sources(s) (e.g. efficiency, lifetime, spectral power distribution, etc.) may deteriorate.

[0040] In particular, for some applications, the light sources(s) of a given lighting unit may be driven with as much current as possible to obtain maximum light output. Such high drive currents invariably raise the temperature of the light source(s), which may diminish the expected lifetime of the light source(s) and reduce their operating efficiency. This is particularly relevant for high intensity LED(s) which dissipate large amounts of heat. An indication of a light source's operating temperature may thus be useful in reducing damage to the light source, in helping prolong its lifetime and/or in maintaining a desired output.

[0041] Furthermore, thermal effects may become increasingly important in a lighting unit combining different light sources, for example of different colors, to produce a combined optical output. Such a lighting unit {e.g. polychromatic lighting unit, white lighting unit, color changing lighting unit, etc.) may experience noticeable, and possibly detrimental effects when the operating conditions of one or more of its constituent light sources begins to diverge due to a change in operating temperature. For example, if the spectral power distribution of a given light source changes due to a temperature increase {e.g. spectral broadening, peak output wavelength shifts, luminous flux output variations and/or fluctuations, etc.), the combined output of the lighting unit {e.g. color temperature, color quality, color rendering index, output intensity, etc.) may also change. For certain polychromatic, white and/or color changing lighting unit applications, such spectral changes may be important, and as such, should be monitored and rectified as best and as quickly as possible. Furthermore, since thermally induced output variations of individual light sources may be different for different colors or for light sources from the same or different lots, it may be beneficial to monitor every light source, or every group, array and/or cluster thereof independently to provide appropriate compensation when needed. [0042] To reduce such thermal effects, for example to reduce or avoid transient color shifts, luminous flux output variations and/or undue damage, the invention provides a lighting unit and a thermal management system and method therefor, configured to assess one or more temperature-dependent characteristics of the lighting unit (e.g. of one of more its constituent parts), and determine the operating temperature of one or more of the lighting unit's light sources. The system may be further optionally configured to responsively adjust one or more operating characteristics of the lighting unit that may affect or be affected by temperature.

[0043] In some embodiments, the determination, management, and optional adjustment of temperature is provided continuously and/or in real time. For example, real-time, or near realtime temperature determination can be provided, as variations in converted light intensity readings, or again in the temperature-dependent characteristics of such readings, can be sensed and reacted to within a relatively short delay. For instance, in some embodiments, the converting element(s) is disposed in close proximity to the light source(s) of which a temperature assessment is desired.

[0044] As introduced above, and in accordance with some embodiments of the invention, a lighting unit includes one or more light sources, and a thermal management system for monitoring an operating temperature of one or more of the light sources, and optionally adjusting one or more operational characteristics thereof in response to variations in operating temperature. The system generally includes one or more converting elements configured and disposed to absorb at least some of the light generated by the light source(s) and emit converted light in response thereto. For example, the intensity of the converted light may, in some embodiments, decay in accordance with a temperature dependent characteristic of the converting element(s), i.e., the converted light intensity may be expressed or at least approximated by a temperature dependant decay function {e.g. exponential decay, hyperbolic decay, etc.). The system further comprises one or more sensing elements configured to sense a first intensity of converted light, and one or more subsequent intensities of converted light during an off-state of the light source(s), for example, such that the temperature dependent decay may be perceived by the sensing elements. Based on these sensed intensities, the thermal management system is configured to determine an operating temperature of the converting element, which, when the converting element is disposed in close proximity and/or in thermal coupling with one or more corresponding light sources, is indicative of an operating temperature of the corresponding light source(s).

[0045] The thermal management system is also optionally configured to adjust one or a number of operational characteristics of the one or more light sources in response to changes in their perceived operating temperature. The adjustments may occur automatically according to a set of pre-determined rules or heuristics, or may be implemented by a user of the thermal management system to adjust operating characteristics in accordance with detected changes in temperature.

[0046] As a general matter, a value representing a first light intensity and a value representing a subsequent light intensity may be used for every determination of the temperature-indicative value and to determine the nature of the change in the light intensity as it relates to time and temperature. In certain embodiments in which the light sources run according to a duty cycle, the first and subsequent light intensity determinations can come from the same cycle or different cycles. In such embodiments, the first value may be determined by either using a first light intensity determined in the current cycle, or an approximation of same by using a first light intensity previously determined in another cycle. The first light intensity may be determined at any point during the on-state portion of a cycle, at a point in time immediately after the on-state portion ends, or during the off-state portion of a cycle. The one or more subsequent light intensity determinations occur (a) during the off- state; and (b) after the point in the current cycle at which a first light intensity determination occurred or, in cases where an approximation of the first light intensity determination is used, after a point in the current cycle that corresponds to the point at which the first light intensity determination was made in a previous cycle. It will be appreciated that readings may be repeated for every duty cycle, or for intermittent cycles, in order to provide for a continuous and/or real-time indication of the temperature of the light source(s) of a lighting unit.

[0047] As will be described in greater detail below with reference to specific embodiments and examples, if the temperature dependent intensity function is known {e.g. via known material characteristic and/or predetermined via system/converting element calibration), then from the first intensity reading and one or more subsequent intensity readings, an estimate at to the temperature of the converting element may be obtained using various mathematical methods and techniques known in the art.

[0048] It will be appreciated that the terms first intensity and subsequent intensity are used herein for the purpose of simplicity of description and can be interpreted to define various combinations of intensity readings taken to identify different values of a temperature dependent intensity function representative of a converting element temperature dependent characteristic.

[0049] FIG. 1 provides a high-level diagram of a lighting unit, generally referred to using the numeral 1000, comprising a thermal management system in accordance with one embodiment of the present invention. It will be appreciated upon reading the following description that the embodiment depicted in FIG. 1 provides only one example of lighting units and thermal management systems therefor contemplated herein, and that variations to this example, some of which are described below in different examples, are not meant to depart from the general scope and nature of the present disclosure.

[0050] Referring to FIG. 1, the lighting unit 1000 comprises one or more light sources 1004, operatively mounted within the lighting unit. The lighting unit further includes a converting element 1020, disposed on an output lens or package of the light source 1004, configured to absorb at least some of the light generated by the light source and emit converted light in response thereto. A sensing element 1006 is also provided for sensing, at least in part, an intensity of the converted light, and communicate a value indicative of this intensity to a thermal management module, depicted herein as thermal management / drive module 1010. In general, the lighting unit will also comprise one or more drive modules {e.g. software, firmware, hardware, drivers, circuitry and/or other such driving means schematically integrated within thermal management / drive module) for driving the lighting unit's light source. In this embodiment, the thermal management / drive module is optionally provided in an operatively integrated manner to drive the light source via drive circuitry 1008, while maintaining an acceptable operating temperature, for example, as monitored via the converting element and sensing element. [0051] It will be readily appreciated by the person of ordinary skill in the art that the converting element may be disposed in a number of different manners, without departing from the general scope and nature of the present disclosure. For example, in the lighting unit 1100 depicted in FIG. 2, the converting element(s) 1120 forms a dispersion within an encapsulation material of the light source 1104, converted light generated thereby being sensed by a sensing element 1106 which is configured to communicate a value indicative of an intensity of the converted light to a thermal management / drive module 1110, as discussed above.

[0052] In the lighting unit 1200 depicted in FIG. 3, and in accordance with another embodiment, the converting element 1220 is provided by a coating on the light source substrate 1202, in this embodiment disposed to absorb a portion of the light back-scattered from the light source 1204. Converted light generated by the converting element is at least in part sensed by a sensing element 1206 which is configured to communicate a value indicative of an intensity of the converted light to a thermal management / drive module 1210, as discussed above.

[0053] In the lighting unit 1300 depicted in FIG. 4, and in accordance with another embodiment, the converting element 1320 is provided by a coating on a LED die of the light source 1304, converted light generated thereby being sensed by a sensing element 1306 which is configured to communicate a value indicative of an intensity of the converted light to a thermal management / drive module 1310, as discussed above.

[0054] It will also be appreciated that, although the above embodiments depict single sensing elements 1006, 1106, 1206 and 1306, respectively disposed toward a periphery of the lighting unit, one or more sensing elements may also be provided in different locations such that converted light is either directly and/or indirectly coupled thereto. For example, in each of the embodiments illustrated in FIGs. 1 to 4, the sensing element is external to a package associated with the light source. This may be beneficial or necessary when the size of the sensing element and/or the restricted space provided within the package are prohibitively mismatched. Clearly, the person of skill in the art will understand that a similar package associated with the light source may be constructed so to include the sensing element on or within the package. [0055] FIG. 5 provides a diagram of a similar lighting unit 200, according to another embodiment of the invention. The lighting unit 200 of this example comprises three light sources 204 operatively mounted within the lighting unit. The lighting unit further includes various converting elements configured to absorb at least some of the light generated by the light sources, or a subset thereof, and emit converted light in response thereto. The lighting unit also comprises different sensing elements, such as sensing elements 206, for sensing the intensity of emitted radiation from one or more of the converting elements and communicate a value indicative thereof to a thermal management / drive module.

[0056] In this embodiment, each of the three light sources 204 are monitored via the sensing element(s) 206. The person of skill in the art will understand, however, that different numbers of light sources may be selected for monitoring without departing from the general scope and nature of the present disclosure. In this embodiment, there is shown a converting element 223 disposed on a die substrate 202 of each light source. Additional or alternative converting elements are also provided as a coating for each light source package 222 {e.g. on a lens thereof), as a coating on the LED die 220 itself, and/or dispersed within the LED package 221, for example, embedded within an encapsulation material or the like. It will be appreciated that one or more of the above examples may be used interchangeably in different embodiments to provide a like effect, as can other examples be considered herein, for instance including a converting element on a lighting unit substrate (not shown) upon which each light source is operatively coupled, without departing from the general scope and nature of the present disclosure.

[0057] In this example, the lighting unit 200 further includes circuitry 208 operatively coupled to the light sources 204 and leading to the thermal management / drive module 210. The thermal management / drive module is generally configured to both monitor and adjust the operational characteristics of each of the lighting unit's light sources in order to manage the temperature thereof, for instance by managing a drive current imparted thereto in response to converted intensity values communicated to the module from the sensing elements 206. For instance, the sensing element(s) are operatively coupled to the lighting unit's thermal management / drive module, which is configured to drive the light sources 204 via circuitry 208, while maintaining an acceptable operating temperature, monitored via the sensing element(s).

[0058] It will be appreciated that, although the present embodiment depicts one or more sensing elements 206 disposed toward a periphery of the lighting unit 200, one or more sensing elements may also be provided in different locations such that converted light is either directly and/or indirectly coupled thereto. For example, in the embodiment illustrated in FIG. 5, the sensing element is external to the light source packages. This may be beneficial or necessary when the size of the sensing element and/or the restricted space provided within the package are prohibitively mismatched. Clearly, the person of skill in the art will understand that a similar light source packages may be constructed so to include a sensing element on or within each respective package, or again within a selected number of these packages.

[0059] It will also be appreciated by the person skilled in the art that there may be more or fewer sensing elements 206 than light sources 204 or converting elements. For instance, each of the one or more sensing elements need not correspond to a respective light source, or converting element associated therewith, as a particular sensing element 206 may operate in conjunction with different numbers of light sources 204 provided it can be optically coupled to a converting element associated with these light sources.

[0060] The exemplary lighting units 1000, 1100, 1200, 1300 and 200, described above and respectively depicted in FIGs. 1 to 5, may further comprise additional elements, such as for example, primary optics (e.g. light source or light source package lens, diffuser, protective coating or covering, light or color filters, etc.), secondary optics (e.g. reflectors, lenses, diffusers, collimators, etc.), and/or other such optical and/or structural (e.g. masks, housing, etc.) elements. The optional inclusion of these and other such additional elements should be apparent to the person of skill in the art and is therefore not considered to depart from the general scope and nature of the present disclosure.

Light Source(s)

[0061] The lighting unit may include one or more light sources in different combinations of types, colors and/or sizes. For example, the lighting unit may comprise a single or single type of light source, for instance comprising light sources of a single color, or comprising two or more different types of light sources providing a combined spectral power distribution, for instance providing light of a given color temperature or quality. Examples of the latter may include, but are not limited to, red, green and blue light sources (RGB), red, amber, green and blue light sources (RAGB), and other such combinations as would be readily understood by the person skilled in the art.

[0062] In general, the one or more light sources may be arranged in one or more groups, one or more arrays or one or more clusters thereof. These light sources may be coated with, or are in close proximity to, a converting element that is capable of absorbing radiation at one or more first wavelength(s) and emitting radiation at one or more second wavelength(s), each of which falling within a same or different regions of the spectrum, such as the infrared, visible and/or ultraviolet regions of the electromagnetic spectrum, for example.

[0063] In some embodiments, the light source(s) is driven in accordance with a given cycle (sometimes referred to by one skilled in the art as a "duty cycle") in which light is emitted from the light source for some duration of time ("on-state") that is followed by a duration of time in which substantially no light is emitted from the light source ("off-state"). In certain embodiments, the respective or common off-state(s) of the one or more light sources may be shorter than is perceptible by the human eye, thereby creating an effect in which no off-state is discernable to the user. Furthermore, the one or more light sources may be in alternating duty cycles in which the off-states do not correspond.

[0064] Furthermore, the person of skill in the art will understand that the one or more light sources may be configured in different numbers and/or types of arrays, groups and/or clusters to provide different effects. Individual light sources, or groups, arrays and/or clusters thereof may be mounted independently or as part of self-contained light source packages comprising various numbers of drive circuits, sensing and/or optical elements.

[0065] In embodiments of the present invention, one or more selected ones of the one or more light sources may be associated with one or more common or respective converting elements, wherein assessing the temperature of only selected light sources can provide a representative assessment of the lighting unit as a whole.

[0066] In some embodiments, each of the one or more light sources are associated with one or more common or respective converting elements to respectively obtain an average light source assessment, or respective light source assessments, for example.

[0067] The person of skill in the art will recognize that a light source may further comprise a lens, protective material, filter, diffuser, or other elements or features known in the art. The material may be composed of glass or transparent polymer or plastic, or other materials. Such a material can serve to, for example, direct or focus light and filter or alter the color of light.

[0068] Each of the one or more light sources in a lighting unit, which may comprise coated elements, non-coated elements, or various combinations thereof, and the one or more sensing elements may be optionally mounted to respective and/or common substrates, such as, for example, a PCB or an embedded semiconductor device. Further, a lighting unit may comprise one or more light source packages, each comprising one or more light sources operatively mounted on a package substrate providing the necessary light source electrode couplings (e.g. electrode pads, traces, etc.) for operating, monitoring and controlling the light source(s). In certain embodiments, one or more light source packages may be mounted on respective and/or common substrates, such as, for example, a PCB or an embedded semiconductor device.

Converting Element

[0069] The one or more converting elements are comprised, in whole or in part, of a substance that is capable of receiving or absorbing radiation, and emitting a converted radiation in response to the absorbed radiation. In general, both the received and the emitted radiation may be characterized by respective wavelengths, which may fall within a same or different regions of the electromagnetic spectrum, for example in the infrared, ultraviolet and/or visible regions of the spectrum.

[0070] Furthermore, the converting element may emit converted radiation having one or more spectral characteristics particular to this converting element, for example having one or more particular peak emission lines and/or bands, and/or one or more particular absorption lines and/or bands. For example, wavelength selective converting materials may be used in order to convert light generated by one or more selected light sources while remaining unresponsive to others. Likewise, converting materials emitting converted light within predefined emission bands may be used in conjunction with sensors and/or filters adapted to detect only those wavelengths of converted light.

[0071] In some embodiments, the converting element may absorb radiation and then emit converted radiation by way of photoluminescence, which may include, but is not limited to, fluorescence and/or phosphorescence.

[0072] In general, the intensity of the converted light generated by the one or more converting elements in response to an optical signal may be characterized by a temporal function, wherein the converted light intensity varies over time once the optical signal is removed. The parameters of this temporal function can generally be associated with one or more characteristics of the converting element, and in particular, to a temperature thereof. Accordingly, by sampling the intensity of converted light over time during an off-state of a corresponding light source, these parameters can be approximated, and the converting element characteristics associated therewith determined.

[0073] In embodiments wherein the temperature-sensitive converting element is disposed in close proximity to, or coated on, a corresponding light source, a value indicative of an operating temperature of the light source may be assessed by sampling the converted light intensity variation during an off-state of the light source, and comparing this sampling with predefined temperature-dependent values or curves for this converting element.

[0074] For example, in an embodiment, the temperature-indicative value is determined by assessing a first intensity and one or more subsequent intensities of converted radiation within a same off-state of a corresponding light source, e.g. near the start and at subsequent times during a same off-state. It will be appreciated that intensity readings may also be used from different off-state cycles to provide a similar effect.

[0075] In some embodiments, the first intensity of converted radiation can be assessed prior to the removal of the excitation source, i.e. during an on-state of a corresponding light source, providing this first intensity can be adequately compared to one or more subsequent off-state intensities to extract the one or more parameters characterizing the converting element's intensity function. For example, in one embodiment, the sensing element is adapted to sense only the converted light (e.g. via an appropriate filter or the like) such that the first intensity is indicative only of a steady state or saturated converted light intensity to which subsequent intensities may be adequately compared providing the start of the off-state is known. In another embodiment, the first intensity will be reflective of both the steady-state or saturated converted light intensity and an intensity of the one or more light sources, in which case, the sensed intensity at the start of the off-state will be marked by a step change that should be accounted for when comparing the first intensity and subsequent intensities.

[0076] As a person skilled in the art would readily recognize, it is possible in certain embodiments to have converting elements correspond to light sources in a one-to-one relationship. It is also possible to have a single converting element for multiple light sources, or multiple converting elements for a single light source.

[0077] In different embodiments, the converting element is a single converting element, or a mixture of different types of converting elements. In some embodiments, the converting element include a phosphor, which generally refers to a substance exhibiting phosphorescence or fluorescence, but may also refer to a substance that exhibits other photoluminescent properties, as will be appreciated by the person of skill in the art. Phosphors, and other such converting elements, can each be characterized in that they have a unique decay time constant. The decay time constant refers to an inherent property of a phosphor and can be described as a value related to the rate at which the intensity of emitted radiation decreases after the removal of excitation energy. A particular type of phosphor generally has a given decay time constant that is unique to it. If the time constant and its dependency on temperature for a particular phosphor is known, then the evaluation of two or more temporally separated converted light intensity readings can be used to determine or approximate a current time constant, and by comparison or extrapolation, a value indicative of the phosphor temperature. It will be appreciated by the person skilled in the art that various mathematical methods and approaches may be used to obtain this value without departing from the general scope and nature of the present disclosure. For example, data comparisons, data fitting and extrapolations, and the like, may be considered to extract the current parameters of the converting elements intensity function, and assess, in light of these parameters, a temperature of the converting element and the light source(s) associated therewith.

[0078] Certain embodiments of the invention include phosphors {e.g. YAG:Ce³⁺) having time constants on the order of 100ns, therefore requiring sensing elements having nanosecond resolution, while others may comprise phosphors (for example, YAG:Cr) with decay time constants of microseconds or longer. Other embodiments of the invention may employ phosphors with even longer decay time constants, in the order of tens of milliseconds, which heretofore have only been known for their use in the state-of-the-art of phosphors and not in the area of light sources.

[0079] The converting element(s) may coat the light source or be placed in close proximity thereto, for example in thermal contact therewith. In certain embodiments, the converting element(s) may form part of a coating or cover of the light source. In other embodiments, the converting element(s) may be dispersed in different media that form additional elements and/or features of the light source, such as an output lens {e.g. hemispherical lens), filter, protective covering, and/or other structural, electrical and/or optical elements as readily understood by the person skilled in the art. For example, when a light source comprises a lens or protective cover, the material used to form the lens or protective cover can contain, or be "doped" with the converting element.

[0080] The converting element may further include, among other photoluminescent materials, a phosphor material, a quantum dot material, a luminescent dopant material or a plurality of such materials. The converting element may further include a transparent host material into which the phosphor material, the quantum dot material or the luminescent dopant material is dispersed.

[0081] Powdered phosphor materials are typically inorganic materials doped with ions of lanthanide (rare earth) elements or, alternatively, ions such as chromium, titanium, vanadium, cobalt or neodymium. The lanthanide elements are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Inorganic materials include, but are not limited to, sapphire (AI₂O₃), gallium arsenide (GaAs), beryllium aluminum oxide (BeAI₂O₄), magnesium fluoride (MgF₂), indium phosphide (InP), gallium phosphide (GaP), yttrium aluminum garnet (YAG or Y₃AI₅O₁₂), terbium-containing garnet, yttrium-aluminum-lanthanide oxide compounds, yttrium-aluminum-lanthanide-gallium oxide compounds, yttrium oxide (Y₂O₃), calcium or strontium or barium halophosphates (Ca,Sr,Ba)₅(PO₄)₃(CI,F), the compound Ce MgAInO ₁₉, lanthanum phosphate (LaPO₄), lanthanide pentaborate materials ((lanthanide)(Mg,Zn)B₅Oi₀), the compound BaMgAIi₀Oi₇, the compound SrGa₂S₄, the compounds (Sr,Mg,Ca, Ba)(Ga, AIJn)₂S₄, the compound SrS, the compound ZnS and nitridosilicate. There are several example phosphors that can be excited at about 250 nm. An example red emitting phosphor is Y₂O₃:Eu³⁺. An example yellow emitting phosphor is YAG:Ce³⁺. Example green emitting phosphors include CeMgAlnOi₉:Tb³⁺, ((lanthanide)PO₄:Ce³⁺,Tb³⁺) and GdMgB₅Oi₀:Ce³⁺,Tb³⁺. Example blue emitting phosphors are BaMgAli₀Oi₇:Eu²⁺ and (Sr,Ba,Ca)₅(PO₄)₃CI:Eu²⁺. For longer wavelength LED excitation in the 400 to 450 nm wavelength region or thereabouts, example inorganic materials include yttrium aluminum garnet (YAG or Y₃AI₅Oi₂), terbium-containing garnet, yttrium oxide (Y₂O₃), YVO₄, SrGa₂S₄, (Sr,Mg,Ca,Ba)(Ga,AI, In)₂S₄, SrS, and nitridosilicate. Example phosphors for LED excitation in the 400 to 450 nm wavelength region include YAG:Ce³⁺, YAG:Ho³⁺, YAG:Pr³⁺, SrGa₂S₄:Eu²⁺, SrGa₂S₄:Ce³⁺, SrS:Eu²⁺ and nitridosilicates doped with Eu²⁺.

[0082] Quantum dot materials are small particles of inorganic semiconductors having particle sizes less than about 40 nanometers. Suitable quantum dot materials include, but are not limited to, small particles of CdS, CdSe, ZnSe, InAs, GaAs and GaN. Quantum dot materials can absorb light at one wavelength and then re-emit the light at different wavelengths that depend on the particle size, the particle surface properties, and the inorganic semiconductor material. Sandia National Laboratories has demonstrated white light generation using 2- nanometer CdS quantum dots excited with near-ultraviolet LED light. Efficiencies of approximately 60% were achieved at low quantum dot concentrations dispersed in a large volume of transparent host material. Because of their small size, quantum dot materials dispersed in transparent host materials exhibit low optical backscattering. [0083] Suitable luminescent dopant materials include, but are not limited to, organic laser dyes such as coumarin, fluorescein, rhodamine and perylene-based dyes. Other types of luminescent dopant materials are lanthanide dopants, which can be incorporated into polymer materials. The lanthanide elements are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. An example lanthanide element is erbium.

[0084] The transparent host materials include polymer materials and inorganic materials. The polymer materials include, but are not limited to, acrylates, polystyrene, polycarbonate, fluoroacrylates, perfluoroacrylates, fluorophosphinate polymers, fluorinated polyimides, polytetrafluoroethylene, fluorosilicones, sol-gels, epoxies, thermoplastics, thermosetting plastics and silicones. Example inorganic materials include, but are not limited to, silicon dioxide, optical glasses and chalcogenide glasses.

[0085] A single type of powdered phosphor material, powdered quantum dot material or powdered luminescent dopant material may be incorporated in the one or more converting elements or a mixture of powdered phosphor materials, quantum dot materials and/or luminescent dopant materials may be incorporated into the converting element(s). Utilizing a mixture of more than one such material is advantageous if a broad spectral emission range is desired for the light of a second wavelength range.

[0086] The converting element(s) may be transparent, translucent or partially reflecting. The optical properties of the converting element(s) depend strongly on the materials utilized for the layer. Converting element(s) containing particles that are much smaller than the wavelengths of visible light and that are dispersed in a transparent host material may be highly transparent or translucent with only a small amount of light scattering. Converting element(s) that contain particles that are approximately equal to or larger than the wavelengths of visible light will usually scatter light strongly. Such materials will be partially reflecting. If the converting element(s) is partially reflecting, it may be embodied as a layer that is made thin enough so that it transmits at least part of the light incident upon the layer. [0087] The converting element(s) may be applied as a coating on the inside surfaces of the light-recycling envelope or substrate, may be applied as a coating on the light output surfaces of an LED, or may partially fill, substantially fill or completely fill the interior volume of any of a number of additional elements or features commonly used in conjunction with light sources, such as output lenses (e.g. hemispherical lens), filters, protective coverings, or other electrical and/or optical elements.

[0088] By placing the converting element(s) in contact, or in close proximity with the emitting layer of a light source, the difference in the temperature between the converting element and the light source will be substantially negligible.

[0089] It will be appreciated by the person skilled in the art that various other examples of converting elements may be considered herein, in different configurations, without departing from the general scope and nature of the present disclosure.

Sensing Element

[0090] The one or more sensing elements are devices that are configured to receive radiation of a particular wavelength, wavelength band or broad spectrum, and measure the intensity thereof. Measurements may generally be made at discrete points in time. As the sensing element(s) has the capability of making rapid measurements in close succession, the sensing element(s) is capable of real-time detection and measurement of radiation. A real-time measurement is generally defined to mean that the measurement reflects the actual state of the thing being measured at, or very near, the time of measurement in an ongoing or continuous manner.

[0091] In general, the one or more sensing elements comprise a device or devices that are configured to receive radiation at one or more pre-determined wavelengths, or a range thereof, and create and transmit a signal related to the intensity of the received radiation. The one or more sensing devices may be configured to assess radiation intensity at a given point in time, and therefore they are capable of determining radiation intensity at discrete points in time or continuously. As a person skilled in the art would understand, it is possible in certain embodiments to have sensing elements correspond to light sources in a one to one relationship. It is equally possible to have a single sensing element for multiple light sources, or multiple sensing elements for a single light source.

[0092] Depending on the type of converting element used, delays between the first intensity and subsequent intensity readings can be on the order of nanoseconds, microseconds or longer. Providing a longer time-period may be desired depending on the level of accuracy and precision that may be required in a particular application, understandably taking into account signal-to-noise ratios, desired light source operations, and other such considerations.

[0093] The one or more sensing element(s) may include different types and/or different numbers of radiation sensing devices, which may include, for example, one or more optical sensors, photodiodes, semiconductor diode detectors, photocapacitors, and/or the like. The one or more sensing elements are generally optically coupled, either directly or indirectly, with one or more common or respective converting elements, the latter being coated on, or in close proximity to, a common, selected or respective light sources to convert light generated thereby, such that sensed converted light intensities may be communicated to the thermal management module to evaluate a temperature of the converting element(s), and light source(s) associated therewith. As a result, the embodiments of the invention allow for a relatively direct and responsive temperature determination of the light source(s) of interest within the lighting unit.

Thermal Management System / Module

[0094] In general, the thermal management system/module is configured to receive signals from the sensing element(s) and interpret same in such a way as to determine a value that is indicative of an operating temperature of the lighting unit's one or more light sources, or subset thereof. This value can be determined at a predetermined time or time interval, or can be determined continuously.

[0095] The temperature indicative values can, for example, be recorded or brought to the attention of a user when certain threshold values are achieved, in response to which, the user may modify the operating characteristics of the lighting unit on an ad hoc basis, for example. Optionally, by using predetermined rules or heuristics, substantially optimal operating conditions of the lighting unit source can be otherwise be maintained automatically, thus preserving the substantially optimal quality and lifetime of a lighting unit.

[0096] Both the one or more light source(s) and the one or more sensing element(s) may be communicatively linked to means for monitoring and optionally adjusting operative characteristics of the one or more light sources. The operative characteristics may include, among others, electrical inputs, the emittance of light, the intensity of light, the duration of light-emittance, the duration of non-light-emittance, the cycle times of light-emittance and non-light emittance, and the regularity or irregularity of said cycle times.

[0097] Each of the light sources in a lighting unit, which may include coated elements, non- coated elements, or any combination thereof, and the one or more sensing elements may be optionally mounted to respective and/or common substrates, such as, for example, a PCB or an embedded semiconductor device. Further, a lighting unit may include one or more light source packages, each comprising one or more light sources operatively mounted on a package substrate providing the necessary light source electrode couplings (e.g. electrode pads, traces, etc.) for operating, monitoring and controlling the light source(s). In certain embodiments, one or more light source packages may be mounted on respective and/or common substrates, such as, for example, a PCB or an embedded semiconductor device.

[0098] In general, there are means to assess the timed intensity measurements, perform calculations, and transmit information related to the received data and performed calculations. Such means may be optionally incorporated as part of the one or more sensing elements, one or more light sources, or as a separate element, which may be mounted to respective and/or common substrates. The means may also be communicatively linked to each of the one or more sensing elements or one or more light sources.

[0099] Information collected by the one or more sensing elements, which are configured to receive radiation emitted from respective and/or various combinations of selected light sources, can be used to determine an operating temperature of the selected light souce(s). In an example embodiment, the light source(s) are operated according to a cycle which comprises a repeating on-state and off-state. In general, a first intensity is determined, followed by a determination of one or more subsequent intensities. As the intensity of the emitted converted radiation changes according to a known temperature-dependent function, a value indicative of the temperature can be assessed using the two or more measurements.

[00100] In some embodiments, the first and/or one or more second determinations of light intensity may comprise singular measurements indicative of individual intensities at a given time. In other embodiments, a determination of light intensity may comprise a single measurement over a fixed time period, thereby providing an indication of the integral or summation of intensities during this time period. For example, a single integrated reading during an off-state could be adequately scaled using a previous on-state reading to provide an evaluation of temperature. In such embodiments, increasing the sampling time (integrated reading rather than singular reading) may allow for the use of slower and less expensive analog- to-digital (A/D) electronics, for example.

[00101] The off-state of a given cycle may be of a duration that is not perceptible to the human eye, thereby providing an opportunity to measure temperature in this manner without affecting the quality of the light emitted from the light sources. The duration of an off-state may be significantly shorter than what would be perceptible to the human eye by one or more orders of magnitude. Also, different light sources may operate according to cycles that are not synchronized, thus enabling duty cycles on individual light sources without a noticeable affect to the quality of the light emitted by the lighting unit. Also, it is not necessary for all light sources in the lighting unit to provide an indication of temperature, as an accurate indication can be obtained by determination in one, some, or all of the light sources in a lighting unit.

[00102] In certain example embodiments, a real-time or continuous temperature of the one or more light sources may be determined when the light sources operate according to a continuous duty cycle. Alternatively, discrete temperature determinations may be made at any desired point in time during one or more selected and/or periodic time cycles.

[00103] In embodiments of the present invention, the monitoring and control means is configured to react to an increase in temperature in one or more selected light sources, and adjust control signals for example in the form of a current, to these light sources to maintain a substantially constant optical output. In another embodiment the monitoring and control means adjusts a current, for example, in order to avoid overheating and thereby reduce the likelihood of damaging the selected light source(s).

[00104] It will be appreciated by the person of skill in the art that various types of monitoring and control means may be considered herein, such as micro-controllers, hardware, software and/or firmware implemented devices or circuitry, and the like, without departing from the general scope and nature of the present disclosure. It will also be apparent to this person that various levels of control may be required based on the desired output and level of accuracy required to achieve this output, thereby affecting the complexity of the driving mechanism, and optional control systems to be implemented in association therewith.

[00105] In some embodiments, the temperature-dependent intensity function of the one or more converting elements can be defined or at least approximated by an exponential decay characterized by a temperature-dependent time constant. For example, in one embodiment, the intensity function of a single phosphor is given by:

I_t = I_oe-"^τ (1)

where I₀ is the initial intensity immediately following removal of the excitation radiation {e.g. at time zero), l_t is the intensity at time t, and τ is the temperature-dependant time constant.

[00106] The decay time constant ris generally defined as the time for the phosphor emission to decay from I₀ to I₀1 e, or approximately 0.368 I₀. Typical time constants for phosphors are 30 to 100 μsec for Eu-based phosphors and are 10 to 30 nsec for Ce-based phosphors. For example, YAG:Ce³⁺ phosphors have decay times less than 100 nsec.

[00107] In some embodiments, an intensity function for a phosphor mixture is provided by a summation of respective exponential decays (e.g. Equation (I)) for each constituent phosphor, each having respective values for I₀ and τ. This summation can generally be approximated by a hyperbolic decay given by:

where a and /?are constants.

[00108] It will be appreciated by the person skilled in the art that, while the above examples employ phosphors reasonably defined by exponential or hyperbolic decay functions, other mathematical means known in the art to model the behavior of the intensity of converted light emitted from a converting element after the removal of a source of excitation may be considered herein without departing from the general scope and nature of the present disclosure. Namely, other types of time constants and mathematical models known in the art would likewise provide the desired operation with the methods and configurations disclosed herein.

[00109] The invention will now be described with reference to specific examples. It will be understood that the following examples are intended to describe embodiments of the invention and are not intended to limit the invention in any way.

Examples

Example 1:

[00110] In one particular exemplary embodiment, the thermal management system includes a sensing element, such as a silicon photodiode, that is connected to a fast analog-to-digital converter or a sample-and-hold amplifier, wherein the sensing element is configured to receive radiation from a phosphor-coated LED. In a first measurement, the sensor output is measured while the LED is energized with a known amount of electrical current. The LED is then de- energized and, following a delay that is approximately equal to the phosphor time constant, a second measurement is performed. If the temperature dependency of the phosphor time constant is known, the ratio of the second measurement to the first measurement will be indicative of the phosphor temperature. If the phosphor coats the LED die, the phosphor temperature will be substantially equal to the LED junction temperature. Given typical YAG:Ce³⁺ phosphor time constants of 100 nsec, the time delay between de-energization of the LED and the second sensor measurement will require a resolution of a few nanoseconds in order to accurately measure the ratio of the second to first measurements. Example 2:

[00111] FIG. 6 shows example data results 2000 of a sensing element residing on a lighting unit measuring the intensity of converted light emitted from a converting element during an interval of time beginning during an on-state of a light source and ending during an off-state of same. The data 2000 may exemplify data obtained for a discrete indication of temperature, or, alternatively, a single cycle within a duty cycle. Readings taken during an on-state 2010 show that the intensity of the light emitted by the light source and the converting element is in a steady or saturated state, i.e. a non-changing condition.

[00112] As illustrated herein by two distinct embodiments A and B, depicted together herein for ease of comparison, the intensity reading immediately after the end of the on-state of the light source shows a characteristic continuous decrease 2040 from a steady-state operating intensity (A), or again, a first step decrease (B) from the steady state operating intensity leading to a substantially same characteristic decrease in intensity 2040.

[00113] For instance, in the example depicted by the embodiment A, light directed to the sensing element may be appropriately masked or filtered such that only converted light is incident thereupon; the sensing element may also or alternatively be configured to respond only, or for the most part, to a given range of wavelengths wherein a peak wavelength of the converted light falls within this range but wherein a peak wavelength of the lighting unit's light source(s) may not.

[00114] Conversely in the example depicted by embodiment B, the sensing element may be configured such that a substantial portion of the light emitted by the light source(s) is sensed thereby, leading to an appreciable step in intensity readings when the light source(s) switches between on and off states.

[00115] As depicted in both embodiments of FIG. 6, during the off-state of the light source, there is a decay in the intensity of the light emitted by the converting element. In this example, the decay follows an exponential decay curve 2040, having a particular time constant defined at a specific temperature. For example, the time constant can be representative of the time at sampling time 2030 in which the intensity is approximately equal to 36.8% of the initial intensity defined at sampling time 2020. In addition, for example, assuming a temperature- dependent time constant for the converting element ( i.e. phosphor), the exponential decay curve 2040 will be shorter or longer depending on the converting element's temperature. Sampling time 2030 therefore defines the sampling time, from which the temperature can be deduced from the ratio of the measured intensity at time at sampling time 2030 to the measured intensity at initial time at sampling time 2020. The equation that can be used to determine the temperature is represented by Equation (1) for exponential decay and Equation (2) for hyperbolic decay. In some embodiments, the ratio versus temperature values are precalculated and stored in a lookup table, which can be accessible by the controller for example, from which the present temperature may be interpolated from the measured ratio.

[00116] In one embodiment, a first assessment of light intensity is performed at the time of initial intensity at sampling time 2020 and a subsequent assessment of light intensity is performed at the end of the time interval beginning at the time initial intensity at sampling time 2020 and having duration about equal to the time constant. In alternate embodiments, the first assessment can be performed at any time during the steady state phase 2010, provided that the magnitude of the step change (applicable to embodiment B only) occurring immediately after the on-state ends at sampling time 2020 is known or is relatively constant.

[00117] In yet another embodiment, the first assessment is performed at a given time during the off-state of the light source, whereas the one or more subsequent assessments occur after the first assessment during this off-state.

[00118] As a person skilled in the art would understand, the first and one or more subsequent assessments can provide a value indicative of the temperature of the converting element, and thus the light source, by comparing the initial intensity at sampling time 2020 and the intensity at about the time constant, or in the alternative, any number of assessments that are performed during the off-state can be used to determine the temperature dependent changes in behavior of the decay of the intensity of the converted light. Example 3:

[00119] FIG. 7 shows further example data results 2100 for a light source or light source package that operates according to a duty cycle. In a particular embodiment, an indication of temperature can be obtained within any of the cycles shown in FIG. 7 according to any of the variations as described above for FIG. 6. Additionally, the temperature indicative values can be assessed during every on/off cycle or periodically according to a pre-determined pattern (e.g., every 5^th cycle), which would provide a continuous indication of the temperature of the light source/package to which a converting element corresponds.

[00120] As a further alternative, the first reading need not be made for every temperature indication. For example, the first reading need only be made in the first cycle (or alternatively, for example, every 10^th temperature measurement) and this value, provided that the change in initial intensity of the converting element is relatively constant, can be used in conjunction with any number of subsequent assessments taken during other cycles in which a temperature indication is desired. Such a variation may provide for a reduction in required computing resources, which may be desired when frequent temperature indications are necessary to determine minor fluctuations in temperature in real-time. For example, a first reading could be taken immediately after the removal of the excitation source (i.e. the light source) during the first cycle 2150 and this value can be used in conjunction with subsequent readings taken at different sampling times during the off-state 2140 in each of the subsequent cycles 2152, 2154, 2156, 2158 and 2160 to obtain an indication of temperature in each cycle. Or again, the first reading can be taken during the first and third cycles and the subsequent readings can be taken in every cycle. Other such variations should be apparent to the person of ordinary skill in the art. In general, such embodiments, or similar variations thereof, may be performed with a fast sample-and-hold amplifier using a slow and inexpensive A/D converter, for example.

[00121] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[00122] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[00123] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[00124] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. [00125] As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[00126] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[00127] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[00128] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively. Also, the reference numerals in the claims are merely for convenience and are not to be read in any way as limiting.

What is claimed is:

Claims

1. A thermal management system for a lighting unit (1000) comprising a light source (1004) configured to generate light, the system comprising: a converting element (1020) configured and disposed to absorb at least some of the light generated by the light source (1004) and emit converted light in response thereto, an intensity of said converted light decaying in accordance with a temperature dependent characteristic of said converting element (1020); a sensing element (1006) configured to sense a first intensity of said converted light, and one or more subsequent decreased intensities thereof during an off-state of said light source (1004); wherein the system is configured to determine, based at least partially on said first intensity and said one or more subsequent intensities, a value indicative of an operating temperature of the light source (1004).

2. The thermal management system according to claim 1, wherein the converting element (1020) is disposed on an output lens or a package of the light source.

3. The thermal management system according to claim 1, wherein the converting element (1020) is dispersed within an encapsulation material optically coupled to the light source (1004).

4. The thermal management system according to claim 1, wherein the light source (1004) is an LED comprising a substrate and wherein the converting element (1020) is a coating deposited on the substrate.

5. The thermal management system according to claim 1, wherein the light source (1004) is a LED die and wherein the converting element (1020) is a coating formed on the LED die.

6. The thermal management system according to claim 1, wherein the converting element (1020) is fabricated with a single converting material or a mixture of different converting materials.

7. The thermal management system according to claim 1, wherein the converting element (1020) comprises a phosphor material, quantum dot material or a luminescent dopant material.

8. A lighting unit (1000) comprising: a light source (1004) configured to emit light; a converting element (1020) configured and disposed to absorb at least some of the light generated by said light source (1004) and emit converted light in response thereto, an intensity of said converted light decaying in accordance with a temperature dependent characteristic of said converting element(1020); a sensing element (1006) configured to sense a first intensity of said converted light, and one or more subsequent decreased intensities thereof during an off-state of said light source (1004); and a thermal management module (1010) operatively coupled to said sensing element (1006) and configured to determine, based at least in part on said first intensity and said one or more subsequent intensities, a value indicative of an operating temperature of said light source (1004).

9. The lighting unit (1000) according to claim 8, wherein the converting element (1020) is disposed on an output lens or a package of the light source (1004).

10. The lighting unit (1000) according to claim 8, wherein the converting element (1020) is dispersed within an encapsulation material optically coupled to the light source (1004).

11. The lighting unit (1000) according to claim 8, wherein the light source (1004) is an LED comprising a substrate and wherein the converting element (1020) is a coating deposited on the substrate.

12. The lighting unit (1000) according to claim 8, wherein the light source (1004) is a LED die and wherein the converting element (1020) is a coating formed on the LED die.

13. The lighting unit (1000) according to claim 8, wherein the converting element (1020) is configured to emit converted light having one or more predetermined spectral characteristics.

14. The lighting unit (1000) according to claim 8, wherein the converting element (1020) is fabricated with a single converting material or a mixture of different converting materials.

15. The lighting unit (1000) according to claim 8, wherein the converting element (1020) comprises a phosphor material, quantum dot material or a luminescent dopant material.

16. The lighting unit (1000) according to claim 8, wherein the thermal management module (1010) is further configured to adjust one or more operational characteristic of the lighting unit (1000) in response to said value.

17. A method for managing operating temperature of a lighting unit (1000) comprising a light source (1004) configured to emit light, the method comprising the steps of: converting at least some of the light generated by the light source (1004) via a converting element (1020) having a temperature dependent characteristic; sensing a first intensity of said converted light during an on state of the light source (1004); sensing one or more subsequent intensities of said converted light during an off state of the light source (1004); and determining a value indicative of an operating temperature of the light source (1004) based at least in part on said first intensity and said one or more subsequent intensities based on said temperature dependent characteristic.

18. The method according to claim 17, wherein the method further comprises adjusting one or more operational characteristic of the lighting unit (1000) in response to said value.

19. The method according to claim 17, wherein the temperature dependent characteristic is defined by an exponential curve or a hyperbolic curve.