WO2014076610A1

WO2014076610A1 - Led-based lighting device and manufacture thereof

Info

Publication number: WO2014076610A1
Application number: PCT/IB2013/059930
Authority: WO
Inventors: Adrianus Johannes Stephanus Maria De Vaan; Stefan Marcus Verbrugh
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-11-16
Filing date: 2013-11-06
Publication date: 2014-05-22
Also published as: WO2014076610A8

Abstract

The present invention relates to a lighting device and a method of manufacturing such lighting devices. The lighting device (100) comprises wavelength converting elements (102,103) which cover first and second portions (202, 203) of a surface(200)of a light emitting diode (101) and are adapted to convert light of a first wavelength (110a) to light of second and third wavelengths (110b-c). Positions (110a, 110b) of the wavelength converting elements relative to each other and to the surface are adjusted such that light emitted by the lighting device as a combination of light emitted via the wavelength converting elements and the uncovered portion (201) of the surface corresponds to a desired color. In some embodiments, the positions are adjusted based on measurements of light emitted by the lighting device. Fig.

Description

LED-based lighting device and manufacture thereof

FIELD OF THE INVENTION

The invention relates to the field of lighting devices comprising light emitting diodes, and methods for manufacturing such lighting devices.

BACKGROUND OF THE INVENTION

Light emitting diode (LED) lamps are growing in popularity and a variety of LED lamp solutions are becoming available. In many LED lamps, several LEDs are combined to achieve certain colors. For example, LEDs of three different colors may be combined to obtain white light. Individual LEDs have slightly different spectral properties so manufacturing of LED lamps usually involves binning procedures in which the spectral properties of light emitted by the individual LEDs are measured and the LEDs are sorted in bins. LEDs from different bins are then combined to form binning kits for use in LED lamps. As several LEDs are needed to achieve a certain color, it may be difficult to simultaneously obtain high color consistency and low etendue.

Wavelength converting materials such as phosphors may be used in LED lamps to convert light emitted from a LED such that other colors than that of the light from the LED may be obtained. However, it would be desirable to provide lighting devices (and methods of manufacturing lighting devices) with alternative and/or improved designs for achieving desired spectral properties of the light output of the lighting devices.

SUMMARY OF THE INVENTION

An object of at least some of the embodiments of the present invention is to provide a lighting device (and a method of manufacturing lighting devices) with an alternative and/or improved design for achieving desired spectral properties of the light output of the lighting device.

This object may be achieved by a lighting device and a method of manufacturing a lighting device as defined in the independent claims. Preferable

embodiments are defined by the dependent claims. According to a first aspect of the present invention, there is provided a method of manufacturing a lighting device. The method comprises the step of covering a first portion of a surface of a light emitting diode adapted to emit light of a first wavelength (or light having a first spectrum), with a first wavelength converting element, wherein the first wavelength converting element is adapted to convert light of the first wavelength to light of a second wavelength (or to convert at least one wavelength component of the first spectrum to a second spectrum). The method comprises the step of covering a second portion of the surface with a second wavelength converting element, wherein the second wavelength converting element is adapted to convert light of the first wavelength to light of a third wavelength (or to convert at least one wavelength component of the first spectrum to a third spectrum). The method further comprises the step of adjusting positions (e.g. lateral positions) of the first and second wavelength converting elements relative to each other and to the surface such that light emitted by the lighting device as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and an uncovered portion of the surface corresponds to a desired color.

According to a second aspect of the present invention, there is provided a lighting device comprising a light emitting diode having a surface adapted to emit light of a first wavelength (or light having a first spectrum). The lighting device comprises a first wavelength converting element arranged to cover a first portion of the surface and adapted to convert light of the first wavelength to light of a second wavelength (or to convert at least one wavelength component of the first spectrum to a second spectrum). The lighting device further comprises a second wavelength converting element arranged to cover a second portion of the surface and adapted to convert light of the first wavelength to light of a third wavelength (or to convert at least one wavelength component of the first spectrum to a third spectrum). Positions (e.g. lateral positions) of the first and second wavelength converting elements relative to each other and to the surface are such that light emitted by the lighting device as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and an uncovered portion of the surface corresponds to a desired color.

The present invention makes use of an understanding that light of a first wavelength emitted from a light emitting diode may be converted into a second wavelength by a first wavelength converting element and to a third wavelength by a second wavelength converting element, and that positions of the first and second wavelength converting elements relative to each other and to the surface may be adjusted such that light emitted by the lighting device as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and an uncovered portion of the surface corresponds to a desired color.

The present invention is advantageous in that a single light emitting diode (LED) may be used to generate a desired color instead of using two or three LEDs, each emitting one color (i.e. light at a single wavelength or with a particular optical spectrum). Using multiple LEDs means that light of the first, second and third wavelengths originate from different light sources and may therefore be affected differently when the LEDs age, so that the color (or other spectral properties) of the light emitted by the lighting device may change. This effect is reduced or mitigated by the present invention since a single LED may be used to achieve the desired color. Moreover, using a single LED may require less space than using multiple LEDs. Furthermore, this reduces the need for optical instruments to mix the light of the first, second and third wavelengths, thereby reducing color variances caused by different light sources. The use of a single LED may also be advantageous in that low etendue may be easier to achieve than with multiple LEDs.

The present invention is also advantageous in luminaires where multiple LED modules (or lighting devices comprising LEDs) are used, and where these LED modules generate light spots that can be physically identified by the human eye, such as e.g. the so called T-LED tubes and similar luminaires. Since the LEDs or LED modules can be physically identified by the human eye, color variations between these modules can become visible. Using LED modules (or lighting devices) according to the invention, the color of all these LED modules become (substantially) identical, or identical within the limitations for visible color variations, by the human eye as normally specified as a low number of SDCM (Standard Deviation of Color Matching, the number of Just Noticeable Differences in color deviation that a standard human observer can identify).

The present invention is also advantageous in spot luminaires where multiple LEDs are required to obtain a sufficient high lumen output. The present invention is advantageous for such systems since the different color elements that contribute to the white beam are adjacent and their angular emission profiles are identical, resulting into only minor color variations in the light beam.

The present invention is also advantageous in that positions of the wavelength converting elements are adjusted such that light emitted by the lighting device corresponds to a desired color. As LEDs originating from a same LED structure during manufacture may present different spectral properties, positions of the wavelength converting elements may be adjusted to compensate for any such differences such that the lighting devices emit light of the desired color. As a result, identical (e.g. of the same material and the same dimensions) wavelength converting elements may be used in combination with LEDs emitting light having different spectral properties, thereby facilitating the manufacturing while still providing lighting devices with a desired color. Accordingly, different wavelength converting elements to combine with different LEDs are not required (and neither is binning of LEDs). Only one set of wavelength converting elements may be used for the manufacture, and adjustments may be done by changing positions of these instead of replacing them by differently dimensioned or differently structured wavelength converting elements.

Another advantage of the present invention is that positions of the wavelength converting elements may be selected both relative to the light emitting surface and relative to each other, which is advantageous as compared to lamps in which the wavelength converting elements would be fixed in relation to each other. Adjusting positions of the wavelength converting elements relative to each other preferably includes a translation and not only a rotation, e.g. at least one of the wavelength converting elements may be translated relative to the other.

The first and second wavelength converting elements cover only part of the entire surface of the LED. The uncovered portion of the surface may be a single part or may e.g. comprise several parts separated from each other by the first and second portions of the surface. The uncovered portion leaves room for altering/adjusting positions of the wavelength converting elements, which is advantageous in that it provides more freedom to control the color of the light emitted by the lighting device and reduces/eliminates the need to replace or modify the wavelength converting elements for achieving the desired color. The uncovered portion may preferably constitute at least 5% of the entire LED surface.

During wavelength conversion of light from a LED, performed by wavelength conversion materials, heat is typically generated, causing efficiency loss. Such efficiency loss will not occur at the uncovered portion of the LED, which is an advantage of lighting devices according to the present invention, compared to lighting devices where the entire surface of the LED is covered by light converting material. Typically, LED lamps have light temperatures varying between 2500 K and 5500 K and for obtaining the desired color, less light is required from the uncovered portion (e.g. blue light) than from the wavelength converting elements (e.g. green and red light). As a consequence, for LED lamps in the range of color temperatures up to at least 6000K (most LED light sources have an intended color temperature below 6000K), and using blue LEDs to drive wavelength conversion materials to convert the blue light from the LED into green, yellow and/or red light, the portions of the LED that need to be covered with these phosphor materials preferably cover a larger area than the uncovered part of the LED. Hence, the different color elements of the LED will typically be closest together when the uncovered portion is located in between the portions of the LED that are covered with a wavelength conversion material.

At least part of the uncovered portion (or the entire uncovered portion) may preferably be located between the first and second portions of the surface. The uncovered portion may preferably be uncovered also by e.g. glass or other translucent material, i.e. a space between the wavelength converting elements corresponding to the uncovered portion of the surface may preferably be empty, or at least empty of solid material such as e.g. glass or other translucent material. For example, the uncovered portion may correspond to a portion of the surface of the LED in which the first and second wavelength converting elements are translatable/movable towards each other.

Light of the first wavelength (emitted from the uncovered portion) may contribute to the light emitted by the lighting device without passing through wavelength converting elements. The lighting device emits light corresponding to a mix of the first, second and third wavelengths even if e.g. no light of the first wavelength is transmitted through the wavelength converting elements (i.e. light of the first wavelength not absorbed by the wavelength converting elements).

The surface of the light emitting diode may e.g. be rectangular, but any other shape may also be envisaged.

The wavelength converting elements may comprise wavelength converting material such as e.g. one or more different phosphors. The wavelength converting elements may have many different shapes, geometries and thicknesses. For example, at least one of the wavelength converting elements may be a plate, e.g. with a rectangular shape. The size of each of the wavelength converting elements may preferably be smaller than half of the surface of the light emitting diode, i.e. such that they may not cover the entire surface, regardless of their positions on the surface.

The lighting device may comprise any number of additional wavelength converting elements covering parts of the surface and adapted to convert light to different wavelengths. Positions, sizes and/or geometries of these may be adapted (e.g. during manufacture) such that light emitted by the lighting device (including contributions from the additional elements) corresponds to a desired color. According to an embodiment, the wavelength converting elements may be arranged at a distance from the surface of the light emitting diode. For example, light emitted from the surface may pass through an open space before reaching the wavelength converting elements. Alternatively, or additionally, at least one of the wavelength converting elements may be comprised in a stack of layers comprising translucent material such as e.g. glass or a lens, wherein at least one of the layers may be located between the surface and the wavelength converting element.

According to an embodiment, adjusting positions of the first and second wavelength converting elements comprises adjusting lateral positions of the wavelength converting elements relative to the surface and/or relative to each other. Lateral positions refer to positions across the surface (or across planes parallel to the surface), e.g. the lateral positions may be described using plane coordinates such as x and y coordinates.

Adjusting positions of the first and second wavelength converting elements may comprise adjusting a lateral position of the first wavelength converting element to adjust the size of the first portion and/or it may comprise adjusting a lateral position of the second wavelength converting element to adjust the size of the second portion. Adjusting the size of the first and/or second portions of the surface enables control of the amount of light of the first wavelength which is converted to the second and/or third wavelength.

The lateral positions of the first and second wavelength converting elements may preferably be adjustable along a common lateral direction. Optionally, positions of the wavelength converting elements may be adjusted along such a common lateral direction only.

Adjusting positions of the first and second wavelength converting elements may alternatively or additionally comprise adjusting a distance between the first and second wavelength converting elements to adjust the size of the uncovered portion of the surface. This distance may be the absolute distance between the two elements (i.e. the shortest possible distance between a point in the first element and a point in the second element) or it may be a distance between certain parts of the first and second wavelength converting elements. For example, one part of the first wavelength element may be adjacent to the second wavelength converting element while another part of the first wavelength converting element may be separated from the second wavelength converting element by a certain distance. In this case, this certain distance may be adjusted by adjusting positions of the first and second elements. In the present example, adjusting a distance between the first and second wavelength converting elements corresponds to adjusting a distance between the first and the second portion of the surface. According to an embodiment, at least one of the wavelength converting elements may extend in a lateral direction outside the outline defining the surface, i.e. only part of the wavelength converting element may overlap the surface of the light emitting diode. For adjusting the lateral position of a wavelength converting element (for the purpose of adjusting the spectral properties of the light emitted by the lighting device), the part of the element residing outside the surface may be increased or decreased. For example, the portion of the surface which is covered by the wavelength converting element may be increased by translating part of the wavelength converting element previously outside the surface towards the centre of the surface.

According to an embodiment, spectral properties (e.g. the color) of the light emitted by the lighting device (as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and the uncovered portion of the surface) may be determined and the positions of the first and second wavelength converting elements may be adjusted based on the determined spectral properties (color). The spectral properties (or color) may e.g. be determined by measuring the spectral properties (or color) using an optical sensor, or by measuring other parameters of the lighting device, such as characteristics/quality of the individual components, power consumption of the LED or heat generated at different positions of the lighting device. In this way, desired spectral properties (e.g. the emitted light corresponding to a desired color) may be obtained for the lighting devices individually. Indeed, the actual light emitted from a specific lighting device may be investigated (determined) and the positions of the first and second wavelength converting elements may be adjusted accordingly. In particular, the positions of the first and second wavelength converting elements may be adjusted to compensate for differences between properties of individual LEDs and individual wavelength converting elements (such differences may occur even if the LEDs/elements are manufactured together during a common process).

The method according to the present embodiment may preferably comprise altering a position of at least one of the wavelength converting elements relative to the light emitting diode if the determined spectral properties (color) deviate from desired spectral properties (color). Whether the position of the first and/or the second wavelength converting elements is to be altered and the amplitude of any such alteration (e.g. translation) may preferably be estimated based on the determined spectral properties or color (of the light emitted by the lighting device) and known properties of e.g. the wavelength converting elements. According to an embodiment, the wavelength converting elements may be fixed (fixated) on the surface (or fixated relative to the surface) when the light emitted by the lighting device corresponds to a desired color.

According to an embodiment, at least part of the light emitting diode and the wavelength converting elements may be enclosed by an envelope (additionally or alternatively, at least part of the uncovered portion of the surface of the light emitting diode may be enclosed by the envelope). The envelope may comprise e.g. glass or any other translucent material and may be arranged to protect the interior of the lighting device. The envelope may be used to adjust the light emitted by the lighting device, i.e. it may comprise e.g. a lens or wavelength converting material. Additionally, or alternatively, the lighting device may comprise power supplying arrangements such as e.g. a socket or wires for connecting the LED to a power source.

According to an embodiment, each of the wavelength converting elements may have one or more edges. Some of the wavelength converting elements may correspond to contours/borders of the first or second portions of the surface of the light emitting diode, i.e. some of the edges may be located in parts of the wavelength converting elements which cover the first and/or second portions of the surface and may therefore define

contours/borders of these regions. During manufacture of the wavelength converting elements, wavelength converting material may be split/cut into pieces such that rough and/or undefined edges are formed. If used in lighting devices, it may be difficult to predict the behavior of light incident to such rough/undefined edges. Hence, an additional

manufacturing step during production of the wavelength converting elements would be desirable, in which at least some of the edges corresponding to the contours of the first and second portions of the surface are shaped so as to form well-defined edges with improved optical properties.

At least one edge of at least one of the wavelength converting elements may include a wall forming an angle relative to the surface of the light emitting diode. The wall may be a flat or curved surface defining the end of the wavelength converting element in at least one direction. The wall may form an angle relative to the surface of the light emitting diode and may preferably be perpendicular to that surface (i.e. with an angle of 90 degrees). Preferably, at least some of the edges defining the contours of the first and second portions of the surface have such walls, whereby these edges provide improved optical properties.

Additionally, or alternatively, at least one edge of at least one of the wavelength converting elements includes a reflective surface. The reflective surface may e.g. include a metal coating or any other reflective material. Preferably, at least some of the edges defining the contours of the first and second portions of the surface include reflective surfaces such that light (emitted from the surface of the light emitting diode) transmitted through in the wavelength converting element and impinging at the reflective surface reflects back into the wavelength converting element. The reflective surfaces may be perpendicular to the surface of the light emitting diode such that light close to the edge of the wavelength converting elements travels the same distance in the wavelength converting elements as light further away from the edges.

According to an embodiment, the second wavelength converting element is arranged on the side of the first wavelength converting element, i.e. it may be adjacent to the first element or it may be laterally separated from it (without overlapping it). In other words, the wavelength converting elements may be arranged more or less in a common plane parallel to the surface of the light emitting diode such that light emitted from the surface of the light emitting diode reaches the second element without passing through the first element (and such that light emitted from the surface of the light emitting diode reaches the first element without passing through the second element). The present embodiment is advantageous in that the lighting device may be made thinner and therefore more compact.

According to an embodiment, at least one (and preferably both) of the wavelength converting elements is adapted to convert (substantially) all light of the first wavelength it receives from the surface. Surfaces only converting part of the incident light may emit light that has different spectral properties at different angles. Indeed, the distance travelled or made by a light ray in a wavelength converting element depends on the incidence angle of the light ray, which affects the spectral properties of the emitted light, causing for instance color over angle effects. An advantage with the present embodiment is to reduce color over angle effects.

According to an embodiment, the surface of the light emitting diode may be adapted to emit light at a first wavelength corresponding to e.g. blue. The first wavelength converting element may be adapted to convert blue light into light of a second wavelength corresponding to e.g. green/lime and the second wavelength converting element may be adapted to convert blue light into a third wavelength corresponding to e.g. red. In the present embodiment, the desired color of the light emitted by the lighting device may be white (as a result of the mix between blue, green and red light).

According to an embodiment, the light emitting diode may be adapted to provide a substantially uniform distribution of light across the surface. According to an embodiment of the present invention, a collection (or plurality) of lighting devices according to any of the preceding embodiments may be provided. In such a collection, the respective relative positions of the wavelength converting elements and surfaces differ (and/or the percentages of the surfaces constituted by the uncovered portions differ, e.g. by at least 1%) between at least some of the lighting devices and the light emitted by the respective lighting devices as combinations of light emitted via the respective first wavelength converting elements, second wavelength converting elements and uncovered portions of the respective surfaces correspond to the same (or identical) color (or the colors of the light emitted by the lighting devices differ by less than what corresponds to a delta in the CIE color space (u', v') of 0,05).

According to an embodiment, an illumination system is provided. The illumination system comprises at least two lighting devices according to any of the preceding embodiments. For at least one of these lighting devices, the position of at least one wavelength converting element relative to the surface of the light emitting diode is different than the corresponding position of a corresponding wavelength converting element in another lighting device of the illumination system.

Alternatively or additionally, the light emitted by the light emitting diodes of at least some of the different lighting devices have different spectral properties, the lighting devices of the collection have a common desired color and positions of the wavelength converting elements are selected to compensate for the differences in spectral properties.

According to an embodiment of the present invention, a luminaire (or luminaire device or lamp) is provided comprising a collection (or plurality) of lighting devices according to any of the preceding embodiments. It will be appreciated that any of the features in the embodiments described above for a method according to the first aspect of the present invention may be combined with other embodiments of methods according to the first aspect of the present invention. Similarly, it will be appreciated that any of the features in the embodiments described above for a lighting device according to the second aspect of the present invention may be combined with other embodiments of lighting devices according to the second aspect of the present invention. Those skilled in the art will realize that features in the embodiments described above for a method according to the first aspect of the present invention may be combined with the embodiments of the lighting device according to the second aspect of the present invention and that features in the embodiments described above for a lighting device according to the second aspect of the present invention may be combined with the embodiments of methods according to the first aspect of the present invention.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, in which:

Figure 1 is a schematic side view of a lighting device according to an embodiment of the present invention;

Figure 2 is a schematic top view of the lighting device in Figure 1 ;

Figure 3 illustrates the surface of the light emitting diode of the lighting device in Figure 1 ;

Figure 4 is a general outline of a method of manufacturing a lighting device in accordance with embodiments of the present invention;

Figure 5 is a CIE 1931 color diagram for illustrating the combination of different wavelengths achieving a desired color of the light emitted by a lighting device according to an embodiment of the present invention;

Figure 6 illustrates a method and/or an apparatus for manufacturing the lighting device in Figure 1 in accordance with an embodiment of the present invention;

Figure 7 is a schematic side view of a lighting device according to an embodiment of the present invention;

Figures 8a-b illustrate an embodiment of a lighting device and the surface of the associated light emitting diode.

Figures 9a-b illustrate an embodiment of a lighting device and the surface of the associated light emitting diode; and

Figures 10 to 12 are schematic side views of lighting devices according to embodiments of the present invention, illustrating different possible types of edges of the wavelength converting elements. Figures 13 to 15 illustrate embodiments of luminaires comprising multiple LEDs (lighting devices) according to the present invention.

Figures 16 and 17 illustrate embodiments for spot lighting devices comprising multiple LEDs (lighting devices) according to the present invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

With reference to Figures 1, 2 and 3, a lighting device 100 according to an embodiment is described. The lighting device 100 comprises a light emitting diode 101 having a surface 300 adapted to emit light at a first wavelength 110a. A first wavelength converting element 102 covers a first portion 302 of the surface and is adapted to convert light of the first wavelength 110a into light of a second wavelength 110b. A second wavelength converting element 103 covers a second portion 303 of the surface 300 and is adapted to convert light of the first wavelength 110a into light of a third wavelength 110c. A portion 301 of the surface 300 is left uncovered between the first portion 302 and the second portion 303 and is referred to as the uncovered portion 301 of the surface 300. A

position 120a of the first wavelength converting element 102 relative to the surface 300 and a position 120b of the second wavelength converting element 103 relative to the surface 300 have been selected (and thereby also a distance between the two wavelength converting elements) such that light emitted by the lighting device 100 as a combination of light emitted via the first wavelength converting element 102, the second wavelength converting element 103 and the uncovered portion 201 of the surface 200 corresponds to a desired color.

In an example, the surface of the light emitting diode 101 is rectangular and the wavelength converting elements 102,103 are rectangular plates (e.g. ceramic plates containing phosphors for converting spectral properties of light). The first wavelength converting element 102 is arranged to partly overlap the surface 300 such that the first portion 302 of the surface covered by the first wavelength converting element 102 is a rectangular left part of the surface 300. Similarly, the second wavelength converting element 103 is arranged to partly overlap the surface 300 such that the second portion 303 of the surface 300 which it covered by the second wavelength converting element 103 is a rectangular right part of the surface 300. The uncovered portion 301 of the surface 300 is rectangular and is located between the first 302 and second 303 portions. Positions of the wavelength converting elements 102,103 in a left-right direction across the surface 300 (and thereby the sizes of the first and second portions 302,303) are selected such that the light emitted by the lighting device 100 corresponds to a desired color. The surface 300 is adapted to emit blue light 110a and the wavelength converting elements 102 and 103 are adapted to convert the blue light 110a into green/cyan light 110b and red light 110c, respectively. The desired color may for instance be white.

With reference to Figure 4, a method of manufacturing the lighting device 100 of Figure 1 , in accordance with an embodiment of the present invention, is described. The method may start with a light emitting diode 101 having a surface 300 adapted to emit light at a first wavelength 110a. One step may be to cover 410 a first portion 302 of the surface 300 by a first wavelength converting element 102 adapted to convert light of the first wavelength 110a into light of a second wavelength 110b. Another step may be to cover 420 a second portion 303 of the surface 300 with a second wavelength converting element 103 adapted to convert light of the first wavelength 110a into light of a third wavelength 110c. Another step may be to adjust 440 positions 120a-b of the first 102 and second 103 wavelength converting elements relative to each other and to the surface 300 such that light emitted by the lighting device 100 as a combination of light emitted via the first wavelength converting element 102, the second wavelength converting element 103 and the uncovered portion 301 of the surface 300 corresponds to a desired color.

Referring to Figure 5, light with different wavelengths may be associated with different color points in a CIE 1931 color diagram. The light emitted by the lighting device 100 includes light of the first wavelength 110a corresponding to a first color point 501, the second wavelength 110b corresponding to a second color point 502 and the third wavelength 110c corresponding to a third color point 503. The color, to which the light emitted by the lighting device 100 corresponds, may be represented by a light mix color point 504 within a triangle having corners defined by the color points 501-503 corresponding to the above-mentioned three wavelengths. The light mix color point 504 may be moved around in the triangle by adjusting positions 120a-b of the first 102 and second 103 wavelength converting elements relative to each other and to the surface 300 (e.g. such that the sizes of the first portion 302, the second portion 303 and the uncovered portion 301 of the surface 300 are varied such that the amounts of light provided at the different wavelengths are varied and the light mix color point 504 is adjusted according to some settings defined by the desired color). With reference to Figure 6, the step of adjusting 440 positions 120a-b of the first and second wavelength converting elements 102,103 relative to each other and to the surface 300 may be performed using an adjustment mechanism 601. The adjustment mechanism 601 may be adapted to adjust a lateral position 120a of the first wavelength converting element 102 relative to the surface 300 and to adjust a lateral position 120b of the second wavelength converting element 303 relative to the surface 300. The lateral position 120a of the first wavelength converting element 102 may be used to adjust the size of the first portion 302 of the surface 300 while the lateral position 120b of the second wavelength converting element 103 may be used to adjust the size of the second portion 303 of the surface 300. The lateral positions 120a-b may be adjustable individually so that they also control the distance 602 between the wavelength converting elements 102,103. The distance 602 may be used to control the size of the uncovered portion 301 of the surface 300.

Figure 6 also shows an intermediate product for manufacture of a lighting device 100. With reference to Figures 2, 3 and 6, the intermediate product comprises a light emitting diode 101 having a surface 300 adapted to emit light of a first wavelength (or light having a first spectrum). The intermediate product comprises a first wavelength converting element 102 arranged to cover a first portion 302 of the surface 300 and adapted to convert light of the first wavelength 110a into light of a second wavelength 110b (or to convert at least one wavelength component of the first spectrum to a second spectrum). The intermediate product further comprises a second wavelength converting element 103 arranged to cover a second portion 303 of the surface 300 and adapted to convert light of the first wavelength 110a to light of a third wavelength 110c (or to convert at least one wavelength component of the first spectrum to a third spectrum). The first and second wavelength converting elements 102 and 103 are arranged to be movable relative to each other and relative to the surface 300 such that, via adjustment of positions 120a-b of the first and second wavelength converting elements 102 and 103 relative to each other and to the surface 300, a lighting device 100 may be obtained which is configured to emit light that, as a result of the combination of light emitted via the first wavelength converting element 102, the second wavelength converting element 103 and an uncovered portion 301 of the surface 300, corresponds to a desired color.

Returning to Figure 4, a method of manufacturing the lighting device 100 may further comprise the step of measuring 430 spectral properties of the light emitted by the lighting device 100. Further, the positions of the first and second wavelength converting elements 102,103 may be adjusted based on this measurement. With reference to Figure 6, the step of measuring 430 spectral properties of the light emitted by the lighting device 100 may be performed by a sensor 603, e.g. a color sensor for measuring to which color the emitted light corresponds (or a sensor measuring e.g. other spectral properties). Further, the adjustment mechanism 601 may be controlled by a control unit 604 receiving information about the measurements from the sensor 603.

Returning again to Figure 4, a method of manufacturing the lighting device 100 may further comprise the step of fixing 450 the wavelength converting elements 102,103 on the surface 300 (or at least fixing their positions relative to the surface 300) when the light emitted by the lighting device 100 corresponds to a desired color. Optionally, the method may further comprise the step of enclosing 460 at least part of the light emitting diode 101 and the wavelength converting elements 102,103 with an envelope 105 (such as e.g. a glass bulb or any other protective screen, optionally comprising a lens). Figure 7 shows the lighting device 100 of Figure 1 further comprising an envelope 105 arranged to enclose the light emitting diode 101 and the wavelength converting elements 102,103.

With reference to Figures 8a-b, another embodiment is described. In the present embodiment, the wavelength converting elements 102, 103 may not be rectangular. For example, the first wavelength converting element 102 may have a rectangular shape but with a recess along one side into which recess the second wavelength converting element 103 may be inserted. The uncovered portion 301 of the surface 300 may comprise one part located between the first portion 302 and the second portion 303 of the surface 300, and other parts located on the side of the wavelength converting elements 102,103. By varying the lateral positions 120a-b of the wavelength converting elements 102,103 the size of the uncovered portion 301 may still be adjusted although the uncovered portion 301 comprises parts not located between the first portion 302 and the second portion 303 of the surface 300.

With reference to Figures 9a-b, another embodiment is described. In the present embodiment the light emitting diode 101 may not be rectangular, but may have any shape such as e.g. a circular shape. Similarly, the first and second wavelength converting elements 102, 103 may have any shape such as e.g. circular. The lighting device 100 may further comprise a third wavelength converting element 104 (or a plurality of additional wavelength converting elements) covering a third portion 304 of the surface 300 and the size of this third portion 304 may be adjusted by adjusting a position 120c of the third wavelength converting element 104. A desired color may then be achieved by adjusting positions of the first, second and third wavelength converting elements 102-104. With reference to Figure 10, a further embodiment of the present invention is described. In some embodiments, the edges 1005a-b of the wavelength converting elements may be rough or undefined so that it may be difficult to predict how light incident to these edges may behave. For example, a first light ray 1006a incident to an edge 1005a may pass through it more or less unaffected, while another light ray 1006b incident to another edge 1005b may be reflected in just about any direction. If such effects are acceptable, wavelength converting elements with undefined edges may be used for keeping the manufacturing process as simpler.

In some embodiments, optical properties of the edges of the wavelength converting elements may be improved by modifying them in different ways. With reference to Figure 11, the edges 1105 a-b located above (i.e. defining a contour of the different portions of) the surface may, according to an embodiment, be arranged to include walls, i.e. flat (or possibly curved) sections at which light may reflect or pass through in a predictable manner. Such a wall preferably forms an angle relative to the surface 200, e.g. it may be an orthogonal or a sloped wall.

With reference to Figure 12, a further embodiment of the present invention is described. In the present embodiment, at least one edge 1205 of a wavelength converting element may include a reflective surface 1207. The reflective surface 1207 is preferably orthogonal to the surface 300 of the light emitting diode 101, thereby enabling a light ray 1206a incident to the reflective surface 1207 from inside the wavelength converting element 102 to be reflected back inside the wavelength converting element 102. With such a reflective surface 1207, a light ray 1206b incident to the reflective surface 1207 from outside of the wavelength converting element 102 may be reflected back outside of the wavelength converting element 102. Consequently, wavelength converting properties of the wavelength converting element 102 are similar for areas close to the edge and those close to the centre of the element, i.e. the color output of the wavelength converting element becomes more uniform than without edges having reflective surfaces.

With reference to Figure 13, a further embodiment of the present invention is described. In the present embodiment, a luminaire 1313 is described comprising a number of LEDs or LED modules (or lighting devices) 1300a, 1300b, 1300c, according to any one of the preceding embodiments. Each LED module 1300a, 1300b and 1300c includes a LED die 1301a, 1301b and 1301c respectively. Each LED die 1301a, 1301b and 1301c may be partly covered with two or a pair of wavelength converting elements 1302a and 1303a, 1302b and 1303b, and 1302c and 1303c, respectively. The LED modules 1300a, 1300b and 1300c, may be mounted on a mechanical carrier 1340, which might be a PCB including electric wiring to feed electric current to the LED modules 1300a, 1300b, 1300c. All LED modules 1300a, 1300b and 1300c, of the luminaire 1313 may be manufactured such that the pairs of wavelength converting elements 1302a and 1303a, 1302b and 1303b, and 1302c and 1303c, respectively, are adjusted on their corresponding LED dies 1301a, 1301b, and 1301c, respectively, such that the color of each module is (substantially) identical within the desired SDCM value.

In Figure 13, it is assumed that the spectral outputs of the individual LED dies 1301a, 1301b and 1301c are different such that the pairs of corresponding wavelength converting elements 1302a and 1303a, 1302b and 1303b and, 1302c and 1303c, respectively, need to be adjusted differently on their corresponding LED dies 1301a, 1301b and 1301c, as indicated by the positioning as depicted in Figure 13.

As a result, the portion of the individual LED dies 1301a, 1301b and 1301c that is left uncovered by the wavelength converting materials is different from one LED module 1300a, 1300b, 1300c, to another. Similarly, the portion of each wavelength converting element that covers the LED dies may vary between the different LED modules.

With reference to Figure 14, a further embodiment of the present invention is described. In the present embodiment, a luminaire 1414 including a LED board 1313 as described with reference Figure 13 (and there referred to as a luminaire) is provided.

Compared to Figure 13, the luminaire in Figure 14 is covered with a diffuser 1415. A wide variety of such kind of luminaires are possible, including embodiments where the diffuser 1415 is part of a tube, and the led modules 1300a, 1300b,and 1300c are all positioned in an elongated stripe forming a T-LED tube.

With reference to Figure 15, a further embodiment of the present invention is described. In the present embodiment, a luminaire 1515 includes two retrofit LED lamps 1516a and 1516b (or lighting devices according to embodiments of the present invention). The luminaire 1515 includes a mechanical frame 1340 that holds two lamp feet 1551a and 1551b. These lamp feet 1551a, 1551b might be conventional ones like E27 standard.

Each of the LED lamps 1516a and 1516b may include a lamp foot 1550a, 1550b for mounting the lamp in the lamp feet 1551a and 1551b, simultaneously providing electrical contacts to provide an electrical current to the lamp. Each of the LED lamps 1516a and 1516b further includes a LED module 1300a, 1300b, each module including a LED die 1301a, 1301b, and each LED die 1301a, 1301b being partly covered with wavelength converting plates 1302a and 1303a, 1302b and 1303b, respectively, and each LED die 1301a, 1301b left partly uncovered by any wavelength converting material. Each of the LED lamps 1516a and 1516b may further include an outer bulb 1552a, 1552b which might carry a diffuser, but may also be made of a fully light transparent material. Each of the LED lamps 1516a and 1516b may further include multiple LED modules such as the LED modules denoted 1301a and 1301b.

In Figure 15, it is assumed that the spectral output of the individual LED dies 1301a, 1301b are different such that the pairs of corresponding wavelength converting plates 1302a and 1303a, and 1302b and 1303b, respectively, need to be adjusted differently on their corresponding LED dies 1301a and 1301b, as indicated by the positioning depicted in Figure 15. As a result, the portion of the individual LED dies 1301a and 1301b left uncovered from wavelength converting materials is different from one LED module 1300a to another LED module 1300b, as it is also the case for the portion of each wavelength converting plate that covers the LED dies. The difference in covered portions is caused by a different position of the wavelength converting material. Moreover, the size of the wavelength material may be equal for all LEDs (or LED modules).

In the present embodiment, all the LEDs in the luminaire 1515 provide identical color (of the emitted light), or identical within a desired SDCM value. As the luminaire 1515 includes retrofit lamps, the individual lamps 1516a and 1516b are exchangeable and a lamp may be replaced with a new lamp. Although the output of the lamps are identical within the desired SDCM specification, individual lamps may vary since the pairs of wavelength converting plates 1302a and 1303a, and 1302b and 1303b may cover different portions of their corresponding LED dies 1301a and 1301b to compensate for spectral differences of the respective LED dies 1301a and 1301b.

With reference to Figure 16, a further embodiment of the present invention is described. In the present embodiment, a spot luminaire 1616 includes a number of LED modules (lighting devices) 1300a, 1300b and 1300c, according to any of the preceding embodiments. The LED modules 1300a, 1300b and 1300c may mounted on a mechanical carrier 1740, which might be a PCB which may also provide an electrical current to the LED modules 1300a, 1300b and 1300c. The spot luminaire 1616 may further include a reflector 1618 to collect the light emitted by the LED modules 1300a, 1300b and 1300c within a desired light beam. The PCB 1740 carrying the LED modules 1300a, 1300b and 1300c, may form a sub module 1717 which may be a sub part provided separately, and adapted to be mounted in a luminaire, as indicated in figure 17. In the examples depicted in Figures 16 and 17, it is assumed that the spectral outputs of the individual LED dies 1301a, 1301b and 1301c are different, such that the corresponding pairs of wavelength converting elements 1302a and 1303a, 1302b and 1303b, and 1302c and 1303c need to be positioned differently on their corresponding LED dies 1301a, 1301b and 1301c, as is indicated by the positioning depicted in Figure 16. As a result, the portions of the individual LED dies 1301a, 1301b and 1301c that are left uncovered by the pairs of wavelength converting elementsl302a and 1303a, 1302b and 1303b, and 1302c and 1303c, respectively, are different between the individual LED modules 1300a, 1300b and 1300c. Similarly, the sizes of the portions of the wavelength converting elements, in the respective pairs, that cover the LED dies vary between the different LED modules.

While specific embodiments have been described, the skilled person will understand that various modifications and alterations are conceivable within the scope as defined in the appended claims. For example, the lighting device may comprise any number of additional wavelength converting elements, and the shapes and/or relative sizes of the light emitting diode and the wavelength converting elements may be combined in any possible way, depending on the desired color.

For example, the term Light Emitting Diode (LED) may cover various technical implementations. A LED could be a semiconductor substrate only, emitting the light spectrum as generated by the semiconductor device (e.g. a narrow spectral band of blue light), but a LED might also be such a semiconductor substrate which is already (entirely) covered with a light conversion layer (phosphor layer) to convert the blue light spectrum into a more whitish one. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures/features are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A method of manufacturing a lighting device (100), the method comprising the steps of:

covering (410) a first portion (302) of a surface (300) of a light emitting diode (101) adapted to emit light of a first wavelength (110a) with a first wavelength converting element (102), the first wavelength converting element being adapted to convert light of said first wavelength to light of a second wavelength (110b);

covering (420) a second portion (303) of said surface with a second wavelength converting element (103), the second wavelength converting element being adapted to convert light of said first wavelength to light of a third wavelength (110c); and adjusting (440) positions (120a-b) of the first and second wavelength converting elements relative to each other and to said surface such that light emitted by the lighting device as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and an uncovered portion (301) of said surface corresponds to a desired color.

2. A method according to claim 1, wherein adjusting positions of the first and second wavelength converting elements comprises:

adjusting a lateral position (120a) of the first wavelength converting element to adjust the size of said first portion;

adjusting a lateral position (120b) of the second wavelength converting element to adjust the size of said second portion; and

adjusting a distance (602) between the first and second wavelength converting elements to adjust the size of said uncovered portion.

3. A method according to any of the preceding claims, further comprising the step of

determining (430) spectral properties of the light emitted by the lighting device, the positions of the first and second wavelength converting elements being adjusted based on the determined spectral properties.

4. A method according to claim 3, wherein, in response to the determined spectral properties deviating from desired spectral properties, altering a position of at least one of the wavelength converting elements relative to the light emitting diode.

5. A method according to any of the preceding claims, further comprising the step of

fixing (450) the wavelength converting elements on said surface when said light emitted by the lighting device corresponds to said desired color.

6. A method according to any of the preceding claims, further comprising the step of

enclosing (460) at least part of the light emitting diode and the wavelength converting elements with an envelope (105).

7. A method according to any of the preceding claims, wherein at least one edge (1005a-b) of at least one of the wavelength converting elements includes a wall forming an angle relative to said surface.

8. A method according to any of the preceding claims, wherein at least one edge (1205) of at least one of the wavelength converting elements includes a reflective surface (1207).

9. A method according to any of the preceding claims, wherein at least one of the wavelength converting elements is adapted to convert all light of the first wavelength it receives from said surface.

10. A lighting device manufactured according to the method of any of the preceding claims.

11. A lighting device (100) comprising

a light emitting diode (101) having a surface (300) adapted to emit light of a first wavelength (110a);

a first wavelength converting element (102) arranged to cover a first portion (302) of said surface and adapted to convert light of said first wavelength to light of a second wavelength (110b); and

a second wavelength converting element (103) arranged to cover a second portion (303) of said surface and adapted to convert light of said first wavelength to light of a third wavelength (110c),

wherein positions (110a, 110b) of the first and second wavelength converting elements relative to each other and to said surface are such that light emitted by the lighting device as a combination of light emitted via the first wavelength converting element, the second wavelength converting element and an uncovered portion (301) of said surface corresponds to a desired color.

12. A lighting device according to claim 11, further comprising

an envelope (105) arranged to at least partly enclose the light emitting diode and the wavelength converting elements.

13. A lighting device according to claims 11 or 12, wherein at least one of the wavelength converting elements extends in a lateral direction outside the outline defining said surface.

14. An illumination system comprising at least two lighting devices according to any of claims 10 to 13, wherein in at least one of the lighting devices, the position of at least one wavelength converting element relative to the surface of the light emitting diode is different than the corresponding position of a corresponding wavelength converting element in another lighting device of the illumination system.

15. A collection of lighting devices according to any of claims 10 to 13.