Etendue conserving, color-mixed, and high brightness led light source

FIELD OF THE INVENTION

The invention relates to the field of Light Emitting Diodes (LEDs) or other light emitting devices and, in particular, to obtain a collimated high brightness etendue conserving LED light source which is colour-tuneable with good colour-mixing properties, and which has a high Colour Rendering Index (CRI).

BACKGROUND OF THE INVENTION

The general lighting market is right now on the verge of undergoing a fundamental change. There is general believe that LED light sources, and especially high power LED light sources, will penetrate the general lighting market, replacing traditional incandescent light bulbs and even fluorescent light tubes, in the near future.

High power white LEDs are often used in consumer lighting products such as spotlights. However, these high power white LEDs suffers, from a consumer point of view, from several drawbacks such as low brightness, low Colour Rendering Index (CRI) (sometimes also called Colour Rendition Index), and the lack of colour tunability, which makes them less desirable in consumer lighting applications.

One way of to obtain colour variable light with high brightness is to stack a number of high brightness LEDs, emitting light in different parts of the spectrum, side by side in a matrix. However, positioning LEDs that emits light with different colours side by side is not an efficient way of obtaining a collimated and good colour mixed light.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve or at least reduce the above given problems and to provide a collimated high brightness etendue conserving, LED light source which is colour-tuneable with good colour-mixing properties, and which have a higher CRI than standard cool-white high power white LED light sources. This object is achieved by a using at least three different coloured LEDs together with a collimated means arranged in accordance with claim 1. Preferred embodiments are defined by the dependent claims.

According to a first aspect of the present invention, there is provided a light system comprising a light source comprised of at least three light emitting elements, at least one collimating means comprised of a base part, an output area, and sidewalls which extends between said base part and said output area, wherein said base part and said sidewalls are made of an light reflective material, and wherein said at least three light emitting elements are placed within said collimating means, at least one dichroic filter transmitting impinging light emitted from at least one of said light emitting elements and reflecting impinging light emitted from at least one other of said light emitting elements, wherein said dichroic filter is situated inside the collimating means. By utilizing this arrangement, and by for instance choosing the three light emitting elements to be high brightness LEDs emitting light with the colours red, green, and blue, a collimated high brightness etendue conserving LED light source with good colour mixing properties can be acheved.

The light system may have at least one dichroic filter arranged to transmit impinging light emitted from said light emitting elements placed at said base part of said collimating means, and to reflect impinging light emitted from said light emitting elements placed on said sidewalls of said collimating means.

This arrangement will enhance the collimation and provide for good colour mixing. The light system may have at least two light emitting elements placed on said sidewalls or said base part, or both, of said collimating means. By placing two light emitting elements, preferably emitting different colours, on each sidewall increase both the brightness of the lighting system and provide for a better colour mixing than if only one light emitting element was used on each sidewall. The light system may comprise an additional collimating means at said base part of said collimating means, arranged so that the light emitted from said light emitting elements, placed at said base part of the additional collimator, is collimated by both said collimating means and said additional collimating means. The additional collimating means will reflect light coming from the light emitting elements placed at the base part of the additional collimating means in such way that less light will be absorbed by the light emitting elements placed on the sidewalls. It will also provide for a more collimated beam of light. The light system may have at least one dichroic filter arranged to transmit impinging light emitted from said light emitting elements placed on at least one said sidewall of said collimating means, and to reflect impinging light emitted from said light emitting

elements placed on said base part of said collimating means. The dichroic filter will reflect light coming from the light emitting elements placed at the base part of the collimating means in such way that no or very little light will be absorbed by the light emitting elements placed on the sidewalls. It will also provide for a more collimated beam of light. The light system may comprise at least three light emitting elements each emitting light with a wavelength corresponding to the colour red, green, or blue respectively. This will provide the opportunity to colour-tune the light source.

The light system may comprise at least three light emitting elements each emitting light with a wavelength corresponding to the colour yellow, magenta, and cyan respectively. This will provide the opportunity to colour-tune the light source.

The light system may have at least three light emitting elements comprised of at least one light emitting diode (LED).

The light system may have at least three light emitting elements comprised of at least one organic light emitting diode (OLED). By using reflective OLEDs most light impinging on the OLED will be reflected, thus increasing the overall brightness of the light source.

It is noted that the invention relates to all possible combinations of features recited in the claims.

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 currently preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Figure 1 shows a cross-section view of a common light emitting diode structure.

Figure 2 shows a cross-section view of a common light emitting diode structure with cone shaped light reflective walls. Figure 3 shows a cross-section view of three light emitting diodes with cone shaped light reflective walls forming a LED light source.

Figure 4 shows a cross-section view of three light emitting diodes situated within a cone shaped light reflecting structure forming a LED light source.

Figure 5 shows a cross-section view of five light emitting diodes situated within a cone shaped light reflecting structure forming a LED light source.

Figure 6 shows a cross-section view of five light emitting diodes situated within a cone shaped light reflecting structure forming a LED light source. Figure 7 shows a cross-section view of five light emitting diodes situated within a cone shaped light reflecting structure forming a LED light source.

Figure 8 shows a cross-section view of three organic light emitting diodes situated within a cone shaped light reflecting structure forming a LED light source.

Figure 9 shows a top view of a hexagonal shaped cone with 16 LEDs placed within forming a LED light source.

Figure 10 shows a three-dimensional side cross-section view of LED light source.

All the figures are highly schematic, not necessarily to scale, and they show only parts, which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows a cross-section view of a common light emitting diode (LED) structure 100. The LED structure comprise a LED-die 102, which in operation is able to emit light of a specific colour depending on the composition of the semi-conducting material used, a dome shaped lens 104 made from glass or any other heat tolerant and optical clear material, a silicon sub-mount 103 mounted on an outer package 101 consisting either of a printed board, with or without a passive thermal heat sink, or a heat sink. When the LED is in operation it will typically emit light up to 90 degrees of a vertical centre axis and the emitted light can either be in the infrared, visible or near-ultraviolet spectrum. Emitted light from the LED-die is illustrated as rays 105, dotted lines with arrows, in the figure. The common light emitting diode structure 100 shown in figure 1 will be used repeatedly throughout the application.

Figure 2 shows a cross-section view of a typical common LED light source consisting of a LED structure 201, a collimated means 205 which in this example is a reflective cone structure shown as two inclined walls in the figure. The reflective cone will reflect and direct the of axis light emanating from the LED-die towards the output area at the top, as illustrated by the light rays 203 in the figure, and produce a collimated LED light

source. The LED light source structure shown in figure 2 is often used in consumer product using a high-powered white LED.

Figure 3 shows a cross-section view of a LED light source consisting of three individual LED light sources 303, 305, and 307. The three LED light sources have LED-dies that are manufactured to emit different colours. In this example, LED light source 303 have a die that emits red light, LED light source 305 have a die that emits green light, and LED light source 307 have a die that emits blue light. Each individual LED light source have its own reflective cone, illustrated by the individual walls 304, 306, and 308 in the figure, which are integrated so that the inclined cone walls intersect each other. The intersecting cone walls are made highly reflective for one colour but transparent for the other two colours. The outer most inclined walls are made reflective for all colours.

For example, LED-light source 305 emits green light that passes through both the walls 304 and 308, which are made transparent to that colour, but is reflected of its own inner walls 306 as indicated by the rays 311 in the figure. In this way a collimated beam of green light is created. In the same manner the light from the red 304 and blue 308 passes through each other's walls but are reflected by its own walls, thus creating collimated red and blue beams of light. In this manner the LED light structure, comprised of the three individual LED lights sources (red, green, blue), will produce a colour-mixed brightness enhanced white LED light source, thus avoiding some of the drawbacks of the single white LED light source presented in figure 2. However, the colour mixing of this arrangement, with all three LED structures placed in the same plane and with intersecting reflective walls, are not optimal.

Figure 4 shows a cross-section view of a currently preferred embodiment of the present invention. In this embodiment the collimating means or reflector structure 400 is shaped as a cone with a flat base part 409 and inclined sidewalls 401. To be able to overcome the shortcomings of using a single high powered white LED light source, three individual LEDs, one emitting red light 403, one emitting green light 402, and one emitting blue light 404, are placed within the cone 400. In this particular embodiment the LED emitting red light 403 is placed at the base part 409 of the cone and the LED emitting green light 402 and the LED emitting blue light 404 are placed on the inner surface of the inclined sidewalls 401. The inner surface of the sidewalls 401 is made highly reflective for all colours.

Inside the reflective cone 400 at the base part 409, another set of walls 405 are placed to completely enclose the LED emitting red light 403. These walls 405 are dichroic colour filters, which are made highly transparent for a specific colour (in this case red) but highly reflective for other colours (in this case green and blue). In this way the LED placed at the

base part 409 of the cone will be able to emit its red light through the dichroic walls 405, as shown by it rays 407, while the rays coming from the other two LEDs 406 and 408, emitting green and blue light, will be reflected as shown in the figure. The red light will be reflected by the inner surface of the inclined sidewalls 401. This arrangement will effectively produce a colour mixed high brightness beam of collimated light as indicated by the rays 406-408 in the figure.

The reflective cone does not have to be shaped as shown in the example in figure 4. Many other cross section shapes can be used such as a U- shape, a V-shape, a U- shape with a flat base, a V-shape with a round base part, or any other useful shape that can act as a collimator for the light.

The reflective cone does not have to be circular (from a top point of view). The cone can be in a circular, oval, or an angular shape. The inclination of the cones cross- section sidewalls 401 can, in combination with the placements of the LEDs on the inclined walls, be varied in a number of ways to produce a specific light source with specific properties. For instance, the angle of the inner surfaces could be chosen in such way that the virtual source of the LEDs on the sidewalls 401, in this case the green and the blue LED, are located on the same position as the red LED at the base.

The dichroic walls 405 do not have to be shaped as an upside-down cone as indicated in figure 4. They can also be in the shape of a pyramid with any number of side surfaces (such as a trigonal, hexagonal, octagonal, etc.), or shaped as a half sphere. Both inner walls of the reflective structure 400 and the dichroic walls 405 can be made to reflect (or absorb) one or more colours.

Figure 5 shows another embodiment of the present invention. In this embodiment two additional LEDs are placed on the inclined walls (501) to improve the colour mixing. Each inclined wall now have one LED emitting blue light 502, 505 and one emitting green light 503, 506. The dichroic walls 507 are in this case made highly reflective for both the blue and the green light, and made transparent for red light as indicated by the rays in the figure. This configuration will enhance the colour mixing and the brightness in comparison to the embodiment presented in figure 4. Figure 6 shows yet another embodiment of the present invention. In this embodiment an additional collimating means (i.e. another cone shaped reflector) 600 has been added to the lower part of the reflective cone 601. The LED emitting red light 604 is now placed in the added reflective cone 600. Also, the LEDs emitting green 603, 606 and blue light 602, 605 on the inclined sidewalls are placed closer together and lower down in the

reflective cone. In this way the of axis red light will be reflected of the closest walls of the added reflective cone 600 as indicated by the rays 608 in the figure, resulting in that less red light hitting the green and blue LEDs are absorbed. This arrangement will also create a more collimated beam of light and it will further enhance the colour mixing and the brightness in comparison to the embodiment presented in figure 4 and 5.

Figure 7 shows yet another embodiment of the present invention. In this embodiment extra filters 707, 708 have been placed in front of the LEDs on the inclined inner walls emitting green 703, 706 and blue 702, 705 light. These filters are made highly reflective for red light but transparent for green and blue light. In this way no red light will reach the LEDs emitting blue and green light, thus reducing the absorption of red light significantly in comparison to previous disclosed embodiments. This arrangement will create a more collimated beam of light than the embodiment presented in figure 6.

Figure 8 shows another embodiment of the present invention where the LEDs have been replaced by Organic Light Emitters (OLEDs). The principle behind the OLED light source is the same as the LED light source discussed in conjunction with figure 4. In this embodiment reflective OLEDs can be used which will act both as reflectors and light emitters. This will improve the overall brightness of the light source.

Figure 9 shows a top view of an example of an application of the preferred embodiment of the present invention. In this example the reflective cone 902 of the LED light source 901 is arranged as a hexagonal with one green 903 and one blue 904 LED arranged on each of the six walls. In the base part of the cone four red LEDs 906 are arranged in a square shape enclosed by hexagonal shaped inner dichroic walls 905.

Figure 10 shows yet another example of an application of the preferred embodiment of the present invention. In this example one or more LED light sources are placed to form a rectangular light assembly emitting a wide collimated beam, at least in one direction, of well colour mixed light.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.