JP5554992B2 - Lighting fixture control system and method - Google Patents

Description

  The present invention relates to the field of lighting, and in particular to controlling the color and intensity of light emitted by a light source.

  Advances in the development and improvement of luminous flux of light emitting devices such as solid state semiconductors and organic light emitting diodes (LEDs) are suitable for use in general lighting applications including architectural, entertainment, and road lighting. I have made it. Light emitting diodes are becoming increasingly competitive with light sources such as incandescent lamps, fluorescent lamps, and high intensity discharge lamps.

  One of the challenges in solid state lighting is a system that can set and maintain the intensity and chromaticity of mixed light emitted by multiple colors, such as, for example, blue and yellow, or red, green and blue LEDs Designing the method. This can be difficult because the light emitted by the LED can vary depending on operating conditions other than the current supplied to the LED. Traditionally, systems that can correct this dependency use optical feedback based on signals provided by one or more optical sensors. This sensor can be used to sense a portion of the emitted light and determine the chromaticity and intensity of the sensed light. Information on chromaticity and intensity can then be used to adjust the LED drive current as appropriate. However, multiple effects must be addressed to enable effective feedback control. For example, first, the spectral responsiveness of known cost-effective RGB color sensors does not reproduce the spectral response of the human eye in sufficient detail for practical purposes. Second, the spectral power distribution (SPD) of the LED can change with the LED operating temperature.

によって表わされる標準的な人である観察者の正規化されたスペクトル応答性を、一般的に商業的に入手可能なＲＧＢ色センサの応答性とともに例証する。センサ特性が標準的な人である観察者の特性に厳密に一致しないことは明らかに確認され得る。スペクトルの不一致は、例示されるものよりも小さいものでも、フィードバック制御の多色ＬＥＤ型システムにおいて不所望な光効果を生じさせ得る。 For example, FIG. 1 shows the CIE color matching function.

Illustrates the normalized spectral responsiveness of a standard human observer represented by the responsiveness of generally commercially available RGB color sensors. It can clearly be seen that the sensor characteristics do not closely match those of a standard human observer. Even if the spectral mismatch is less than that illustrated, it can cause unwanted light effects in feedback controlled multicolor LED type systems.

As is well known in the art, the SPD denoted by Φ (λ) is converted to the corresponding CIE tristimulus value by determining the average of the weighted SPD using the corresponding color matching function. obtain. This can be expressed in terms of the above CIE color match function by the following formula:

  Such tristimulus values determined based on signals supplied by an RGB color sensor with insufficiently accurate responsiveness may not provide a practically useful indication of CIE tristimulus values. As is well known, other color matching functions can also be used to determine the corresponding stimulus values in the corresponding color space.

  A known approach, as exemplified in US Pat. No. 6,507,159, discloses a method and system for controlling a luminaire based on RGB LEDs that tracks both feedback and reference tristimulus values in a specific manner. The forward current that drives the LED luminaire is adjusted based on the comparison between the feedback tristimulus value and the reference tristimulus value until the comparison value does not produce any difference between the two. Tristimulus values are determined using specific filter sensor combinations. However, even under temperature controlled laboratory conditions, matching filters and sensors to accurately reproduce the CIE color matching function is complex. Therefore, it is described in “GPEppeldauer,“ A Reference Tristimulus Colorimeter, ”Proceedings of the Ninth Congress of the International Color Association of the Optical Engineering Society, SPIE 4421, pp749-752, (2002), Bellingham, WA, USA”. Useful filter sensor combinations can be expensive. Further, feedback control based solely on CIE tristimulus values does not separate chromaticity (ie, color) from intensity, and therefore may not be effective in suppressing a large number of undesirable chromaticity variations.

を波長範囲によって

及び

へ分割する方法、及び、このことがいかにＲＧＢセンサに関するスペクトル応答性要件を簡素化するかを説明している。Barnesは、

を規定し、ここで、l及びsは、長波長領域及び短波長領域を表わす。実験室品質の器具以外に関して、従来技術において、

及び

スペクトル応答性の両方を表わすために青色フィルタ検出器対応答の適切なスケールのものを使用することが通常の慣行である。しかし、この対処法は、動作時において、ＲＧＢセンサスペクトル応答性の不一致の不所望な効果を軽減させる方法を対処していない。 BTBarnes is a color matching function in "A Four-Filter Photoelectric Colorimeter," Journal of the Optical Society of America 29, (10), pp 448-452, (1939).

Depending on the wavelength range

as well as

And how this simplifies the spectral responsiveness requirements for RGB sensors. Barnes

Where l and s represent the long wavelength region and the short wavelength region, respectively. For non-laboratory quality instruments, in the prior art,

as well as

It is normal practice to use an appropriate scale of the blue filter detector pair response to represent both spectral responsiveness. However, this remedy does not address a method that reduces the undesirable effects of RGB sensor spectral responsiveness mismatch during operation.

  BAWandell and JEFarrell published RGB sensor data in "Water into Wine: Converting Scanner RGB to Tristimulus XYZ" Device-Independent Color Imaging and Imaging Systems Integration, Proc. SPIE 1909, pp 92-101, (1993). In the calibration step, a method for converting to XYZ tristimulus values by using a transformation matrix that can be pre-determined from the least squares method is described. The calibration step utilizes data from an ideal CIE color match sensor, and calibration data from a non-ideal RGB sensor is obtained from a group of SPD measurements per sensor. However, Wandell does not teach the use of the least squares method with a real-time feedback device or its application to light source control. The transformation is applied only to the measured RGB color sensor data for each pixel of the image.

  GDFinlayson and MSDrew described the above mentioned Wandell et al. In "" Constrained Least-Squares Regression in Color Spaces, "Journal of Electronic Imaging 6, (4), pp 484-493, (1997). A method similar to the method of dealing with will be described.

  FIG. 2 shows an example of SPD of light emitted by an RGB LED module at two different operating temperatures, but otherwise under the same static operating conditions. The ambient temperature is one at 25 ° C and the other at 75 ° C. In addition to the effects of different operating temperatures, different LED drive currents in different color LEDs can result in different ratios of power loss and consequently different LED junction temperatures. This means that when comparing SPDs, the different peak wavelengths shift and the different SPDs spread differently, so that the chromaticity of the mixed light changes nonlinearly depending on the drive current and operating temperature of each LED It can be made clear that it can cause In addition, temperature coupling between different colored LEDs can cause interdependencies between LED junction temperatures. As a result, the well-known Grassman's law of color additivity mixes without taking into account the thermal effects of half of any optical sensor used to sense the LED and generated light and the cloth. It cannot provide an accurate description of the color of light. Thus, luminaire feedback control systems can suffer from a number of effects including the problem that RGB sensors with different sensitivities apply different intrinsic responses to the same SPD light. Changes in the SPD of the colored LED described above can also cause variations in the response of the RGB sensor. Thus, variations in RGB sensor signals in response to variations in SPD can also be unique. In addition, RGB sensors that approximate the ideal sensor may provide different signals compared to the ideal sensor in response to the same SPD. Furthermore, the responsiveness of the RGB sensor can vary depending on its temperature.

  Accordingly, there is a need for a luminaire controller system and method that can effectively control the light generated by the luminaire.

  This background information is provided by the applicant to disclose information that may be relevant to the present invention. No admission that any of the above information constitutes prior art to the present invention is necessarily intended and should not be so construed.

  An object of the present invention is to provide a lighting control system and method. According to one aspect of the invention, a method is provided for controlling one or more light emitting elements (light emitting elements) driven by a forward current to produce mixed light. The method includes obtaining sensor data representing the mixed light, supplying set point data representing the desired mixed light, and converting the sensor data into first data represented by coordinates in a predetermined color coordinate system. A step of converting, a step of converting the set point data into second data represented by coordinates of the predetermined color coordinate system, and comparing the first and second data to determine between the first and second data Determining a difference between the first and second data, and adjusting the forward current in response to the difference between the first and second data to reduce the difference between the first and second data.

  According to another aspect of the invention, a system is provided for controlling one or more light emitting elements (light emitting elements) driven by a forward current to produce mixed light. The system includes one or more optical sensors that acquire sensor data representing the mixed light, a user interface that supplies set point data representing the desired mixed light, and the sensor data in coordinates of a predetermined color coordinate system. Is converted into first data represented, and further, the set point data is converted into second data represented by coordinates of the predetermined color coordinate system, and the first and second data are compared, and the first data is compared. Determining a difference between the first and second data, and further adjusting the forward current in response to the difference between the first and second data to reduce the difference between the first and second data. A controller, wherein the controller is configured to reduce the difference between the first and second data until the absolute value of the difference falls below a predetermined threshold.

FIG. 1 shows the normalized spectral response of a standard human observer represented by a CIE color matching function, and a group of responsiveness of commonly commercially available RGB color sensors. FIG. 2 shows two SPD examples for RGB LED modules operated at ambient temperatures of 25 ° C. and 75 ° C. FIG. 3 shows the architecture of a feedback and control system for a light emitting element based luminaire according to the present invention. FIG. 4 shows an example of recursive triangulation of the RGB color space according to the present invention. FIG. 5 shows a block diagram of an exemplary light emitting element operating temperature compensation method according to an embodiment of the present invention. FIG. 6 shows a block diagram of an exemplary process for an exemplary white mode conversion in accordance with an embodiment of the present invention. FIG. 7 shows a block diagram of an exemplary gamut mapping process for chromaticity mode conversion according to an embodiment of the present invention. FIG. 8 shows a block diagram for an exemplary common conversion method according to an embodiment of the present invention. FIG. 9 illustrates a feedback and control system using a PI control scheme according to an embodiment of the present invention.

Definitions The term “light emitting element” (light emitting element) refers to an electromagnetic spectrum such as, for example, the visible light region, the infrared light and / or the ultraviolet light region, when activated by applying a potential difference across it or passing an electric current. A device that emits radiation in a region or combination of regions. Thus, the light emitting elements can have the properties of monochromatic, pseudo-monochromatic, multicolored, or broadband spectral emission. Examples of light-emitting elements are semiconductor, organic or polymer / polymer light-emitting diodes, optically-excited phosphor-coated light-emitting diodes, optically-excited nanocrystalline light-emitting diodes, or other similar, as can be readily appreciated by those skilled in the art Including equipment. Further, the term light emitting element is used to define a particular device that emits radiation, such as an LED die, and the particular device that emits radiation and one or more such particular devices are arranged. It can equally be used to define a combination with a housing or package.

  As used in this document, the term “about” refers to a +/− 10% variation from the rated value. It should be understood that such variations are always included in any value provided in this document, whether specifically referenced or not.

  Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

  The present invention provides a feedback and control system that controls the current supplied to one or more light emitting elements in a luminaire. The feedback and control system may incorporate an optical sensor that senses a portion of the light emitted by the light emitting element and a user interface for information exchange with the user and the temperature sensor system. The temperature sensor system may further comprise a light emitting element junction temperature sensor system that monitors the temperature of the light emitting element, and optionally a sensor temperature system that monitors the temperature of the optical sensor.

  In accordance with the present invention, the feedback and control system can be configured such that the particular signals used by them correlate with the color and intensity of light at the coordinates of the predetermined desired color space that is selected. The degree of correlation can be directly linearly proportional. These signals may include system input and output signals, as well as signals derived from these signals by conversion to a predetermined desired color space. These signals may include signals indicative of system set points. The system set point describes the desired output of the system and can be changed by the user during operation, thereby triggering a transition between the two desired states. The system can be configured to perform transitions in a number of common predetermined ways.

  For feedback control, the output and set point signals can be compared to determine the difference between the two. The difference is usually considered as the deviation of the output from the set point. Each difference in this case determines the change to the corresponding electrical drive current for each group of light emitting elements that is required to reduce the difference between the corresponding instantaneous output of the luminaire and the desired output. Used to. Therefore, the information encoded in the setting signal or sensor signal or both needs to be available in a common color space before they can be compared. Thus, either one or both of the signals may need to be converted to the selected common color space. According to the present invention, the common color space is the predetermined desired color space described above. Generally, the controller is configured to adjust the drive current to the light emitting element in response to a comparison of the instantaneous output and the desired output. In accordance with an embodiment of the present invention, the drive current is calculated as the difference between feedback RGB sensor data representing instantaneous output and set point RGB data describing the desired output, the absolute value of the difference being less than the desired threshold. It is adjusted to reduce until it becomes.

According to an embodiment of the present invention, the common color space may be defined by the responsiveness of the optical sensor at certain predetermined operating conditions of the optical sensor. Specifically, each of the responsiveness can be used as a basis function of a coordinate system used to define a predetermined desired color space.
It is noted that the instantaneous output mentioned above refers to the output when the light emitted by the light emitting element of the luminaire is interacting with the corresponding sensor. The instantaneous output is usually processed later and the delay depends on the nature of the feedback system. As is known, the instantaneous value of the feedback signal when it is actually processed typically depends on the time it takes to propagate the output signal through a portion of the feedback system until it is processed by the feedback and control system, Corresponds to previous output. In digital control systems, additional delays can occur because samples of the output signal that are fed back can only be taken at intervals or at specific times. Delays in the feedback and control system can also result from holding data from the sampled signal in the storage device until processed.

  According to one embodiment of the present invention, the feedback and control system is configured to convert RGB sensor data to a reference data coordinate system and compare the two. According to another embodiment, the feedback and control system is configured to convert the reference data into a coordinate system of RGB sensor data and compare the two. According to another embodiment, the feedback and control system is configured to convert the reference data and RGB sensor data to coordinates in a predetermined color space that is different from both the reference data and RGB sensor data color spaces. In general, feedback and control systems output or sample signals and setting signals to reduce the difference between RGB sensor data and the reference RGB data until the absolute value of this difference falls below a predetermined threshold. In response to the comparison, the forward drive current to the light emitting element is adjusted.

Feedback and Control System Control Method and Dynamics According to the present invention, for example, when the feedback and control system processes an input or set point, or output signal, such as to determine an output deviation from a set point. At any time, information regarding specific operating conditions and operating modes of the system may need to be considered. The system can be in a static mode of operation where the system input and output parameters that are apparent to the user do not change, or the system operates in a transition mode where the output parameters change as a result of changes to the input parameters. obtain. Although input and output parameters do not change, internal system parameters and variables that describe the state of the system or its components can change. The transition mode includes, for example, a case where the color or intensity of light emitted by the luminaire transitions from an initial value to a desired target value. As a result, the feedback and control system needs to detect and properly handle system conditions even when the transition mode is enabled.

  In accordance with the present invention, for example, the digital feedback and control system changes the color or chromaticity or both in incremental steps of a predetermined or dynamically determined size until a predetermined output is achieved. Transitions can be performed in an iterative manner. If a transition is in progress and a command requiring a new transition is received, the feedback and control system may wait for the completion of the initial transition before initiating a new transition. Alternatively, the system may update the transition parameters while the initial transition is running, and adjust the timing of the transition, if necessary, so that it can be achieved according to a predetermined or desired schedule. Different embodiments may take advantage of these different approaches in various combinations.

  The control system may also perform overlapping transitions in a time multiplexed manner and may be configured to complete, update or even suspend one or more of the ongoing transitions in a predetermined manner. The control system can also be configured to synchronize overlapping time multiplexed transitions to obtain the desired lighting effect. Different embodiments may be configured to perform stepped transitions at different ratios or frequencies. For example, stepwise intensity adjustment can be performed at 50 Hz.

  Since the feedback and control system determines a new drive current for the light emitting element of the luminaire, the feedback and control system is the maximum drive current that the drive current can tolerate according to the design and operating conditions of the entire system including the luminaire at that moment It can also be verified that it does not exceed. In accordance with an embodiment of the present invention, the feedback and control system may reduce the drive current from the initial determined value to prevent one or more effects that may be undesirable or harmful to system components including lighting fixtures. Such effects can include, for example, overheating, flicker, and unwanted color drift due to increased intensity. The drive current can be reduced in a number of different predetermined ways that can vary depending on the particular cause or effect to be mitigated. This means that the drive current for one or more light emitting elements needs to be reduced to prevent overheating of the light emitting elements, so the light emitting elements themselves may not overheat, but for example, the desired chromaticity It may include dimming that needs to be dimmed to maintain.

  It is noted that the drive current can be provided in a number of different formats including, for example, analog or pulse formats. The pulse format may include pulse width modulation, pulse code modulation, or pulse density modulation drive current. The pulsing scheme encodes additional information in the light generated in response to the drive current, to improve time-average drive current resolution, to suppress unwanted flicker at low average drive currents, or for example. It is also noted that additional modulation by frequency, amplitude, or pulse duration can be made. Thus, drive current control and scaling can be a matter of adjusting, for example, the pulse width, pulse amplitude, or pulse density of the drive current. It is noted that different embodiments may use one of these or other well-known digital and analog drive current control schemes or combinations thereof.

  The system can perform intensity transitions based on a perceptual linear form such as, for example, square law or logarithmic dimming, or other alternative desired predetermined dimming curve Can be used.

  For improved stability and response time, the feedback and control system is configured to change a number of internal control parameters in a predetermined manner that depends on the magnitude of the drive current or the strength of the feedback or sensor signal. obtain. The internal control parameter may be a calibration factor that determines the corresponding proportional integral differential (PID) signal or other known parameters that can be adjusted to affect the dynamics of the feedback and control system. For this purpose, the feedback and control system can acquire and maintain data about characteristic operating conditions, which can be utilized for self-calibration purposes and control improvements. Different embodiments store this data in non-volatile memory and perform a self-temperature assessment based on a predetermined scheme, such as when operating within a range of predetermined operating conditions or at a predetermined interval or frequency, for example. obtain.

  Architecture of luminaire-based systems using feedback and control systems

  FIG. 3 shows the architecture of a feedback and control system for a light emitting element based luminaire according to the present invention. The luminaire includes one or more light emitting elements to generate light. The light emitting element 40 is electrically connected to the power supply 30 via the current driver 35. The power supply 30 may be based on, for example, an AC / DC or DC / AC converter. A luminaire that includes a multicolored light emitting element may include a separate current driver for each color. Separate current drivers can be used to provide different forward currents to light emitting elements of different colors at a point in time.

  One or more RGB sensors 50 are provided that can be calibrated to sense the luminous flux output of the light emitted by the luminaire. In one embodiment, a separate light sensor 50 is provided for each color of the light emitting element 40. In addition, a color filter may be associated with one or more color sensors 50. Each RGB sensor 50 is electrically connected to an amplifier / signal converter 55 that can convert the sensed signal into an electrical signal that can be processed by the control system 60.

  As shown, control system 60 may control the amplification and integrated control signals of amplifier / signal converter 55. It will be understood that each RGB sensor 50 is sufficient to provide a stable photocurrent and can detect the amount of luminous flux that provides a signal with an appropriate signal to noise ratio. The RGB sensor 50 can be shielded to prevent stray or ambient light from being sensed by this sensor. However, alternative embodiments may be configured to detect ambient light, for example.

  The user interface 65 is coupled to the control system 60 and provides information about the desired color temperature, chromaticity and / or desired luminance flux output for the luminaire from the user or, for example, a programmable 24 hour timer, a theater lighting console or one of ordinary skill in the art. Provides means for obtaining from other control devices, such as other suitable devices, as can be readily understood by. The overall system, including the user interface, can be configured in a number of different ways that allow different ways to control the light emitted by one or more luminaires. Possible system configurations range from allowing the user to change the emitted light directly, to entering information to pre-program a lighting program that can be automatically executed by the system at a desired time and interval, etc. Can give.

  Information provided by the user interface is converted into an appropriate electrical reference signal for use by the control system 60. The control system 60 can thereby determine an appropriate control signal for transmission to the current driver 35 to obtain the desired luminance flux and chromaticity of the light produced by the luminaire. The control system 60 can be a microcontroller, a microprocessor, or other digital signal processing system that can be readily understood by those skilled in the art.

  In one embodiment, and as shown in FIG. 3, the control system 60 can optionally be operably coupled to one or more light emitting element temperature sensors 45. The light emitting element temperature sensor 45 provides information regarding the temperature of the light emitting element 40 under operating conditions. In this case, information regarding the temperature of the light emitting element 40 can be used to compensate for temperature induced luminance flux variations and characteristic light emitting element specific temperature induced peak center wavelength shifts.

  For example, the temperature of the light emitting element 40 is determined by measuring the forward voltage of the light emitting element, by measuring the resistance of a thermistor in thermal contact with the light emitting element, or by measuring the voltage of the thermal coupling. Can be done. As a result, the control system 60 can control the current driver 35 to adapt the drive current for the group of light emitting elements 40 in a feed forward manner.

  Similarly, one or more temperature sensor elements 45 may provide information about the operating temperature of the optical RGB sensor. This information can be used to account for temperature dependent changes to the spectral response of the optical sensor and to compensate for unwanted response effects.

  For one embodiment, the control system 60 is responsive to signals from both the RGB sensor 50 and the temperature sensor 45 because the digital feedback control system 60, which is responsive only to the light sensor 50, has a constant luminous flux. And low long-term stability in maintaining chromaticity.

  According to embodiments of the present invention, the temperature sensor element may be a forward voltage sensor system or other temperature sensor element that determines the operating temperature of the light emitting element of the luminaire. As shown in FIG. 3, an embodiment of the control system may be configured to process signals provided by one or more voltage sensor elements 70. The voltage sensor element is operatively connected to the light emitting element of the luminaire to sense the forward voltage of the light emitting element 40. As can be known in the art, the voltage sensor signal is processed based on the instantaneous drive current of the corresponding light emitting element to determine the junction temperature of the light emitting element. For example, the voltage sensor signal may be filtered with a bandpass filter having a center frequency equal to about twice the center frequency of the AC line frequency. The control system 60 may optionally sample the voltage sensor continuously to measure residual ripple current that may result from incomplete power supply filtering, and undesired effects on the luminous flux output from the light emitting element 40. In order to reduce this, the duty cycle of the PWM drive signal to the drive device 35 can be adjusted. The sampling frequency of the voltage sensor signal can typically be configured to be greater than about 300 Hz in order to minimize visual flicker.

  The present invention may be described below with reference to specific examples. It will be understood that the following examples are intended to illustrate embodiments of the invention and are not intended to limit the invention in any way.

及び、３×３の変換行列

を用いて制御システムをプログラミングすることによって実行され得る。N^Tは転置であり、N^＋はNの偽逆数である。Mは理想的三刺激値M_ijのn×3行列であり、Nは、n個のＳＰＤの同一セットに関するＲＧＢ色センサデータの対応するn×3行列である。M及びNは、n個のＳＰＤを活用する較正ステップにおいて決定され得、これらを、Ｎを決定するためにＲＧＢ色センサを用いて、及び、例えば、Ｍを決定するために正確に較正されたすスペクトロメータを用いて、特徴付け得る。Tは、その後、例えば、エラー関数

を最小化することによって、例えば最小二乗法などにより、決定され得る。この方法は、トレーニングセットのＳＰＤに関して測定された理想的なセンサデータと測定されたＲＧＢセンサデータとの間の三刺激値空間における平均ＲＭＳ値を抑制する手段を提供し得る。較正処理において得られたTを用いるＳＰＤの［R G B］から得られる［X Y Z］は、線形補間近似であることを特記される。 Example 1
In a first example, the control system reads RGB sensor data [RGB] and derives the appropriate values for the CIE tristimulus values X, Y and Z of the light emitted by the light emitting element. It may be configured to apply a transformation. This is, for example, a linear algebraic relationship

And 3 × 3 transformation matrix

Can be implemented by programming the control system using. N ^T is the transpose, and N ⁺ is the false reciprocal of N. M is an n × 3 matrix of ideal tristimulus values M _ij and N is the corresponding n × 3 matrix of RGB color sensor data for the same set of n SPDs. M and N may be determined in a calibration step that utilizes n SPDs, and these were accurately calibrated using RGB color sensors to determine N and, for example, to determine M It can be characterized using a spectrometer. T then, for example, an error function

Can be determined, for example, by the least squares method. This method may provide a means to suppress the mean RMS value in the tristimulus value space between the ideal sensor data measured for the training set SPD and the measured RGB sensor data. It is noted that [XYZ] obtained from [RGB] of SPD using T obtained in the calibration process is a linear interpolation approximation.

であり、強度は、ＣＩＥ三刺激値Ｙによって表わされる。一つの実施例において、制御器は、異なる所定の行列T_xyYを用いて、［R G B］値を、直接色度座標x、y及び強度Yを有する座標空間［x y Y］へ変換するように構成され、この場合、

である。 As is well known in the art,

And the intensity is represented by the CIE tristimulus value Y. In one embodiment, the controller is configured to convert [RGB] values directly into a coordinate space [xy Y] having chromaticity coordinates x, y and intensity Y using a different predetermined matrix T _xyY. And in this case

It is.

  It is noted that each group of RGB values is associated with a specific chromaticity and intensity. If the gain of the RGB sensor is scaled sufficiently linear with intensity for practical purposes, the desired change in intensity can therefore be realized by the control system by appropriately scaling all RGB values.

  In addition, error functions other than Equation 5, such as the sum of absolute value differences, can also be used. Furthermore, each of the values in the [X Y Z] and / or [R G B] matrix may be given different weights in the error function to obtain different desired control effects.

として与えられる。 The minimization process may use a coordinate space other than [XYZ]. It is noted that the CIE 1931 chromaticity coordinates x and y are perceptually non-linear and it may be advantageous to linearize x and y in a perceptual sense when the color feedback system controls the light source. The For example, the CIE 1976 Uniform Chromaticity Scale (UCS) color space coordinates provide this form of linearization, according to (CIE 2004)

As given.

であるＣＩＥＬＡＢなどの、他の知覚ＵＣＳへ変換することも可能であることを特記される。このことは、より複雑な処理を必要とし得る、三刺激値の非線形な変換を伴う。 The coordinates [u ′ v ′ Y] can therefore be used in embodiments of the present invention. Measurement standard is color difference

It is noted that conversion to other perceptual UCSs such as CIELAB is also possible. This involves a non-linear conversion of tristimulus values that may require more complex processing.

  The advantage of using xyY or u'v'Y coordinates for color feedback control is that color and intensity are represented separately. Thus, the desired change in intensity can be achieved by scaling Y without requiring additional calculations in xy or u′v ′. Separation into uncoupled colors and intensities that can be varied practically independently without substantially affecting another is undesirable due to the quantization of floating point calculations in digital processing Can help reduce chromaticity shifts.

Example 2
In another embodiment, operating the control system directly with feedback raw RGB sensor data may be advantageous with respect to computational efficiency. In such an embodiment, the control system no longer needs to convert the RGB sensor data each time it is shared. Instead, user-specific input data is converted from coordinates such as XYZ tristimulus values or xyY chromaticity and intensity to RGB sensor coordinates, for example, for the control system to compare setpoints with RGB color feedback data. . In such an embodiment, the conversion needs to occur only when the user specific input data changes. In this embodiment, the control system operates on RGB sensor coordinates to set and maintain the desired chromaticity and intensity.

から決定され得る。数式１１において使用される変換Tは、上述されるように決定されることを特記される。代替的に、T^-1は、数式５において使用されるＲＧＢ色空間座標におけるＲＧＢ値よりむしろ、XYZ色空間座標において規定される対応する色関数を用いることを除いて、上述と同一な手法で直接決定され得る。 For a given transformation T, the target RGB value is

Can be determined from It is noted that the transformation T used in Equation 11 is determined as described above. Alternatively, T ⁻¹ is in the same manner as described above, except that it uses the corresponding color function defined in the XYZ color space coordinates, rather than the RGB values in the RGB color space coordinates used in Equation 5. Can be determined directly.

0 ≦ R _T ≦ R _max , 0 ≦ G _T ≦ G _max , and 0 ≦ B _T ≦ B _max , and R _max , G _max, and B _max are when the light emitting element is operated at full power If it is the maximum reachable value for the corresponding RGB color sensor output, the user specific XYZ or other, eg, xyY value is in the color and intensity gamut of the light emitting element. If any of these conditions are not met, the specified color and intensity cannot be reached by the light emitting element.

Example 3
In this embodiment, the controller converts each of the one or more predetermined RGB sensor data to a corresponding predetermined desired color space, such as XYZ data, while the training set of RGB sensor data. The rest is transformed as described above even if the mean least squares error for the rest of the data is increased. This embodiment can be used to ensure that the control system can perform a calibration process that maintains such white RGB sensor data.

によって決定され、ここで、T_jはTのj番目の列であり、M_jはMのj番目の列であり、M_wは［1 1 1］である。 An additional limitation on the calibration method may be expressed as M _w = N _w T, where N _w is the RGB sensor data for a given “white” SPD and M _w is the corresponding XYZ tristimulus value. It is. The transformation matrix is

Where T _j is the j th column of T, M _j is the j th column of M, and M _w is [1 1 1].

  In one embodiment, the controller is configured with CIE 1976 UCS color space coordinates u ′ and v ′ and intensity Y that support CIE tristimulus values XYZ.

であり、これが、この実施例に関する全ての実用目的及びＲＧＢセンサデータに関して許容可能に小さいようにされる。 Example 4
In an embodiment of the present invention, a least squares format may be used for conversion between color coordinate systems. Both the least squares method and the restricted least squares method are linear affine transformations between RGB coordinates and XYZ tristimulus values coordinates. This implicitly ensures that the nonlinearity of the LED driver and the RGB color sensor is sufficiently small, so that the maximum error is

This is made to be acceptable small for all practical purposes and RGB sensor data for this embodiment.

For example, if ΔE _max exceeds a predetermined threshold, the color gamut of the RGB light emitting elements in the RGB color space coordinates can be subdivided. This can be facilitated by increasing the number of sample points for interpolation and using finer sample rasters in the color space. This can be facilitated, for example, as illustrated in FIG. FIG. 4 shows an example of recursive triangular subdivision in the RGB color space. Corresponding target coordinates, such as u′v ′ or u′v′Y, of the vertices of each triangle t can in this case be used for calculating one transformation matrix T _t for each triangle t. A group of RGB color space coordinates within the color gamut of the light emitting element can then be contained within one particular triangle, in which case it can be transformed with respect to this triangle using a transformation matrix T _t .

One aspect to consider when determining the transformation matrix {T _t } is that adjacent pairs of these matrices are data along a common edge and vertex, and one of the two matrices is an RGB vector transformation. Conversion to the same target coordinates, regardless of whether they are used in This can be facilitated by using appropriate boundary conditions for the error function when determining the least squares method for the triangulated grid.

For example, given a measured RGB vector, it is necessary to determine which triangle it occupies and thus which transformation matrix should be applied. An exemplary method is as follows:

Input: R, G, B
const n = 4
Array: M [n] [n] [n]

// Normalize RGB sensor values
Rnorm = R / Rmax
Gnorm = G / Gmax
Bnorm = B / Bmax

// determine array index
x = R * n / (R + G + B)
y = G * n / (R + G + B)
z = B * n / (R + G + B)

// Determine transformation matrix index
t = M [x] [y] [z]

Where n = 2 ^s and s is the level of recursive subdivision, and M is a three-dimensional array with stored triangle indices. About three quarters of the array elements can be invalid because they cannot be indexed by xyz. If it is necessary to save memory, M can be stored as a sparse array using known computer technology, or the array can be implemented programmatically using a decision tree. A recursive triangle approach is also described in US Pat. No. 7,140,752, where the multivariate function defining a hyperplane representing constant intensity intensity and chromaticity is a piecewise linear function rather than a radial function. Is represented by

Example 5
In the embodiments described above, the control system can be optionally combined using temperature compensation methods. As noted, the SPD of the light emitting element and the channel gain of the RGB color sensor can exhibit significant temperature dependence. As a result, the RGB color sensor data may depend on the operating temperature of the light emitting elements, and possibly the operating temperature of the RGB sensor, where these dependencies are identified in one or more of the transformation matrices described above. Can be done.

  In one embodiment, the temperature dependence of the SPD and RGB channel gains can be linearly interpolated over the full range of operating temperatures, and the control system can determine the transformation matrix for the given one or more low operating temperatures and the given one or more. May be constructed using another one or more transformation matrices for a high operating temperature of In this case, converting RGB sensor data to, for example, u'v'Y or xyY at one or more measured temperatures is a problem of linearly interpolating converted RGB sensor data for high and low temperature conversion. is there. In this embodiment, the feedback system may be provided with means for obtaining the temperature of the light emitting element and / or the RGB sensor. With respect to the operating temperature between these extremes, two groups of color feedback system parameters can be determined using both matrices, and the desired parameters can be linearly interpolated between these values for each color channel.

  In another embodiment, the control system may be configured to interpolate in a piecewise linear fashion within each group of predetermined adjacent operating temperature intervals. The operating temperature interval can cover the complete desired range of operating temperatures. This can help mitigate the generation of perceptible lighting artifacts caused by linear interpolation over a full range of operating temperatures using only one interval.

FIG. 5 shows a block diagram of an exemplary light emitting element operating temperature compensation method according to an embodiment of the present invention. In the first step, for example, the light emitting element operating temperature is determined based on a signal obtained from a temperature sensor or a forward voltage sensor. With respect to digital processing, it is noted that the sensor signal can be converted from analog to digital form. The light emitting element operating temperature for an RGB type light emitting element luminaire having a corresponding number of sensors can be determined according to the following table.

For white light, additional temperature correction factors can be calculated. This correction factor may consist of temperature calibration at two points in the blackbody locus. These constants can in this case be varied linearly over the trajectory based on the mirek input of the current target CCT. An illustrative example of this calculation is shown in the table below.

The above correction factor for white light, which is generally calculated for a given CCT or Mirek value, in this case, in order to calculate the appropriate luminous element temperature correction using the formula in the following table according to an embodiment of the present invention: Can be applied.

  Similar calculations can be performed for colored light, as will be apparent to those skilled in the art.

Similarly, temperature compensation of the sensor signal can be used in embodiments of the present invention. Signals that can be converted from analog to digital using an A / D converter can be obtained from a number of different temperature sensors. The following table provides an example of the use of the temperature correction sensor signal in accordance with an embodiment of the present invention.

In another embodiment of the invention, the temperature compensation of the sensor signal can be approximated based on the set point S _{(R, G, B)} instead of the actual instantaneous sensor signal. In this embodiment, sensor temperature compensation is as follows:

P _{TC (R, G, B)} = T _PHD × S _{(R, G, B)} × T _{PK (R, G, B)} -Dk _{(R, G, B)}

Can be defined as follows.

In this embodiment, the _{PTC (R, G, B)} constant can be updated more quickly because this constant is based on the set point rather than the instantaneous signal.

Example 6
It is well known that the sensitivity of the human eye to changes in light intensity is non-linear. In other words, a relative change in intensity is not perceived as the same relative change in brightness. Rea, M., Ed. 2000 is the second to linear brightness dimming in "The IESNA Lighting Handbook", Ninth Edition. New York, NY: Illuminating Engineering Society of North America, p. 27-4. A method using multiplicative dimming is described. As is known, perceptual linear dimming can be achieved by normalizing and squaring the desired intensity. In order to achieve perceptual linear dimming using a multicolor light source such as an RGB LED-based luminaire, first determine the initial ratio of color intensity and then obtain the same chromaticity at the desired new intensity. These ratios need to be maintained during dimming in order to be able to be maintained. In one embodiment, the control system may be configured for squared dimming using the following process.

Input: Rt, Gt, Bt

// Normalize RGB target values
Rnorm = Rt / Rmax
Gnorm = Gt / Gmax
Bnorm = Bt / Bmax

// find the maximum
max = Rnorm
IF Gnorm> max
max = Gnorm
ENDIF
IF Bnorm> max
max = Bnorm
ENDIF

// Square RGB normalized value
Rnorm = Rnorm * max
Gnorm = Gnorm * max
Bnorm = Bnorm * max

// Output squared RGB values
R = Rnorm * Rmax
G = Gnorm * Gmax
B = Bnorm * Bmax

Example 7
As is well known, Glassman's law of color additivity is satisfied in any linear color space, such as CIE 1913 chromaticity, CIE 1976 UCS, or luminaire specific RGB. Therefore, in order to smoothly fade between two user specific colors, it is sufficient to interpolate the chromaticity linearly along a straight line between the two specified colors. However, this may require floating point instructions when executed in a microcontroller or similar processing system and may slow down the performance of the control system. For real time fading between initial and desired target colors and intensities, therefore, for example, "" Radiosity: A Programmer's Perspective "by Ashdown, New York, NY: John Wiley & Sons, pp. 200-202, (1994 It is useful to interpolate along a straight line using a differential digital analyzer algorithm such as

Example 8
In another embodiment, such as suitable for applications that require the generation of white light, the control system uses an adjacent set of linearized intervals for each section of the blackbody locus that covers the desired color temperature range. Can be configured. In this case, smooth white light fading between two user specific color temperatures (CT) linearly interpolates the chromaticity along a piecewise linearized black body locus between the two user specific color temperatures CT. Is executed. In one embodiment, CT intervals along the blackbody locus can be evenly spaced at reciprocal color temperatures. The unit commonly used in the art is 10 ⁻⁶ K ⁻¹ , also referred to as (microreciprocal Kelvin) or mirek unit. In this case, linear interpolation in the CIE 1976 UCS color space is approximately equivalent to linear interpolation in inverse CT, and the system uses a practical relevant countermeasure, for example, quantified with Mirek for convenience. Can be calibrated.

Example 9
For applications that require near maximum luminous flux output from the luminaire, the following method can be used.

Input: Rt, Gt and Bt

const Rmax, Gmax, Bmax
var Rnorm, Gnorm, Bnorm
var scale
var max

// Determine the maximum target RGB value
max = Rt
IF max <Gt
max = Gt
ENDIF
IF max <Bt
max = Bt
ENDIF

// Normalize RGB values
Rnorm = Rt / max
Gnorm = Gt / max
Bnorm = Bt / max

// determine the scaling factor
scale = Rnorm / Rmax
IF scale <Gnorm / Gmax
scale = Gnorm / Gmax
ENDIF
IF scale <Bnorm / Bmax
scale = Bnorm / Bmax
ENDIF

// Maximize RGB target value
Rt = Rnorm / scale
Gt = Gnorm / scale
Bt = Bnorm / scale

Here, Rt, Gt, and Bt are target RGB values before intensity dimming is applied. This algorithm may ensure that red, green and blue LEDs are operated at approximately maximum intensity and user specific color in the absence of intensity dimming.

を計算することによって達成され得、ここで、

であり、各行列要素は、赤、緑及び青色発光要素が全強度で動作される場合に関する生成される対応ＲＧＢセンサ値に対応する。 The target RGB value needs to be converted into a pulse width modulation duty factor D for the light emitting element driver described above, or equivalently, a current multiplier for the analog light emitting element driver. This means

Which can be achieved by calculating

And each matrix element corresponds to a corresponding RGB sensor value generated for the case where the red, green and blue light emitting elements are operated at full intensity.

  In accordance with embodiments of the present invention, input intensity scaling with operating temperature may be required for two different reasons. In general, the intensity is limited to the lower of the two obtained limits. The first intensity scaling results from the light emitting element operating temperature being limited. According to an embodiment, if the light emitting element temperature exceeds a predetermined maximum light emitting element operating temperature, such as 90 ° C., the maximum allowable intensity is scaled down according to a predetermined temperature reduction table. An exemplary table is given below. This ensures that the light emitting element temperature does not exceed the maximum light emitting element temperature, regardless of chromaticity or intensity set point. For practical purposes, it is noted that the emission junction temperature cannot exceed a temperature estimated from a dedicated temperature sensor located in the vicinity above a specific offset temperature, such as about 10 ° C. Thus, the temperature de-rating table can be limited to about 80 ° C. However, the junction temperature of the light emitting element can be inferred directly from the forward voltage, which can make it unnecessary to consider temperature offsets in the configuration of the feedback control system.

  In the PWM control embodiment, the second intensity scaling algorithm may guarantee constant chromaticity when one of the PWM channels reaches its maximum value. In one embodiment, the maximum allowable intensity is decremented when the PWM level reaches the first threshold. The maximum intensity can be incremented when and when the maximum PWM value falls below the second threshold.

In general, as described above, the system may typically use the lower of the two acceptable intensity values described above. The following table outlines the intensity reduction and provides exemplary threshold and scaling values according to an embodiment of the present invention.

Example 10
As described above, various data and parameters are handled by the feedback control system. 6, 7 and 8 provide further details regarding one aspect of the data conversion, representation and variant embodiments of the present invention. The schematically illustrated embodiment of the method used includes three different types of data including local parameters, persistent attributes and global variables. Local parameters are indicated by solid arrows and represent function call parameters that are passed for use only in a given function. Persistent attributes are indicated by dotted arrows, are managed by a separate control management firmware module, and are maintained in non-volatile storage. Global variables are indicated by bold arrows and include global range temporary variables required by various firmware modules. These embodiments can be implemented in firmware.

  FIG. 6 shows a block diagram of an exemplary process for white mode conversion used as part of the method used to generate white light. This method includes a CCT (correlated color temperature) color gamut reduction process and a CCT interpolation process. The process may be used to map input CCTs or chromaticities that exceed the luminaire color gamut back to corresponding achievable CCTs and chromaticities.

The CCT color gamut reduction process ensures that the requested CCT is in a range that can be supported by the luminaire. The data can be calibrated with Mirek and implemented as described in the table below.

According to one embodiment, the CCT interpolation process is used to map input CCT values to set values for one or more optical sensors. The interpolation process outlined in the following table is therefore performed for each color channel, eg, three times for an RGB-based luminaire, to calculate the target sensor signal in the target color space.

FIG. 7 shows a block diagram of an exemplary gamut mapping process for chromaticity mode conversion used as part of the method used to generate colored light of desired chromaticity in the color space. The chromaticity mode conversion is similar to the CCT conversion shown in FIG. The gamut mapping process is used to map back / reduce input chromaticities that are outside the gamut of the luminaire to neighboring chromaticities within the gamut. An exemplary embodiment using u'v 'chromaticity coordinates is shown in the table below.

The color interpolation module shown in FIG. 7 is used to output a target color point, such as, for example, R _t G _t B _t and can be implemented in some embodiments as described in the following table.

  FIG. 8 shows a block diagram for an exemplary common conversion method used in both the color and white conversion mode methods described. The following table provides an illustrative example of each sub-module of the common conversion method.

Intensity transitions can be implemented and implemented as described in the following table.

Chromaticity transitions can be implemented and implemented as described in the following table.

R _t G _t B _t scaling may be performed and implemented as described in the following table.

Example 11
An exemplary embodiment of a feedback and control system using a PI (proportional-integral) feedback control scheme is shown in FIG. The example may be implemented using the formulas provided in the following table. As illustrated, this embodiment does not derive a derivative (D) from the difference signal between the set point and the instantaneous output. It can be readily appreciated that there are multiple alternative P, I or D control element combinations.

  It will be appreciated that the above-described embodiments of the invention are illustrative and can be modified in many ways. Such present or future changes should not be construed as departing from the spirit and scope of the present invention, and all such modifications as will be apparent to those skilled in the art are included within the scope of the appended claims. It is intended to be included in the scope.

Claims (18)

A method of controlling one or more light emitting elements driven by a forward current to produce mixed light comprising:
a) obtaining sensor data representing the mixed light;
b) providing set point data representing the desired mixed light;
c) converting the sensor data into first data represented by coordinates in a predetermined color coordinate system;
d) converting the set point data into second data represented by coordinates of the predetermined color coordinate system;
e) comparing the first and second data to determine a difference between the first and second data;
f) adjusting the forward current in response to the difference between the first and second data to reduce the difference between the first and second data;
Have
And a step of repeating steps a) to f) until the absolute value of the difference falls below a predetermined threshold value.
The sensor data is provided by one or more optical sensors, each optical sensor providing responsiveness at a predetermined operating condition of the corresponding optical sensor, each responsiveness being one of the predetermined color coordinate systems. It defines a basic function,
The conversion of the sensor data into the first data in step c) is one or more of sensing information about the temperature of the optical sensor provided by one or more temperature sensors and / or a forward voltage of the light emitting element. Depending on the signal provided by the voltage sensor,
Method.   The method of claim 1, wherein the predetermined color coordinate system corresponds to a CIExyY chromaticity coordinate system.   The method according to claim 1, wherein the predetermined color coordinate system corresponds to a CIEu'v'Y chromaticity coordinate system.   The method of claim 1, wherein the sensor data includes information representing a weighted average of one or more response functions.   The method of claim 1, wherein the setpoint data is provided via a user interface. The method according to claim 1, linear change in intensity of the mixed light, when represented by the predetermined color coordinate system, corresponding to substantially linear perceived intensity variations of the mixed light, Method.   The method of claim 1, wherein the sensor data is provided by a predetermined number of sensors, the predetermined number corresponding to a number of different nominal colors of the one or more light emitting elements. .   The method of claim 1, wherein transforming the sensor data includes performing a first linear transform.   The method of claim 1, wherein transforming the set point data includes performing a second linear transform. 10. A method according to any one of claims 1 to 9 , for use in a feedback control system. A system for controlling one or more light emitting elements (light emitting elements) driven by a forward current to produce mixed light,
a) one or more optical sensors for obtaining sensor data representative of the mixed light;
b) a user interface for supplying set point data representing the desired mixed light;
c) converting the sensor data into first data represented by coordinates in a predetermined color coordinate system; further converting the set point data into second data represented by coordinates in the predetermined color coordinate system; Control comparing the first and second data to determine a difference between the first and second data, and further adjusting the forward current in response to the difference between the first and second data And
Including
The controller is configured to reduce the difference between the first and second data until the absolute value of the difference falls below a predetermined threshold;
Each of the one or more optical sensors provides a responsivity at predetermined operating conditions, each responsivity defines one basis function of the predetermined color coordinate system,
The conversion of the sensor data into the first data in c) is one or more of sensing information about the temperature of the optical sensor provided by one or more temperature sensors and / or a forward voltage of the light emitting element. Depends on the signal provided by the voltage sensor,

system. 12. The system according to claim 11 , wherein the predetermined color coordinate system corresponds to a CIExyY chromaticity coordinate system. 12. The system according to claim 11 , wherein the predetermined color coordinate system corresponds to a CIEu'v'Y chromaticity coordinate system. 12. The system according to claim 11 , wherein the sensor data includes information representing a weighted average of one or more response functions. A system according to claim 11, linear change in intensity of the mixed light, when represented by the predetermined color coordinate system, corresponding to substantially linear perceived intensity variations of the mixed light, system. 12. The system of claim 11 , wherein the sensor data is provided by a predetermined number of sensors, the predetermined number corresponding to a number of different nominal colors of the one or more light emitting elements. . 12. The system of claim 11 , wherein converting the sensor data includes performing a first linear transformation. 12. The system of claim 11 , wherein converting the set point data includes performing a second linear transformation.

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