EP2583024B1 - Light source - Google Patents

Description

A light source with light emitting diodes (LEDs) is indicated.

This patent application claims the priority of the German patent application 10 2010 023 956.9 , the disclosure of which is hereby incorporated by reference.

Lighting devices with LEDs and in particular with an LED cluster with different colored LEDs, such as blue, green and / or red LEDs are nowadays usually arranged compactly, wherein the individual adjacent LEDs have a certain distance, also referred to as "pitch", the due to building and / or thermotechnical reasons can not be fallen below. Furthermore, the total number of LEDs is usually limited due to the heat emitted by the LEDs during operation with respect to a maximum operating temperature of the lighting device.

For example, assuming a typical lighting device for producing white light having a color temperature of about 4000 K, it may have, for example, about 21 green or mint green and about 5 red LEDs. The red LEDs are needed in particular to increase the so-called color rendering index (CRI). Due to the above considerations regarding the arrangement of LEDs and the small number of red LEDs compared to the green LEDs, the spacing of the red LEDs in one maximizes Cluster with uniformly distributed red and green LEDs.

If an object is illuminated with such a lighting device, such as a hand or a pencil, then an observer in the shade that the object casts in the light of the illumination device can reveal color inhomogeneities, so-called color shadows or color patterns, and luminance inhomogeneities, so-called luminance shadows or luminance patterns perceived by the small number of red LEDs and their large distance from each other within the LED cluster of the lighting device caused.

In order to minimize the color shadows and luminance shadows, significantly more LEDs would be required, but this is not possible technically or only with great effort for the reasons mentioned above with regard to the heat development of the illumination device.

In " The IESNA Lighting Handbook, 9th ed., 2000, Illumination Engineering Society of North America, New York, pages 3-18 and 3-19 It is shown that the spatial resolution of the human eye after 800 ms observation time is about 0.6 arc minutes. Discrete luminance differences must therefore have smaller spatial resolutions so as not to be perceived as disturbing by an observer.

In particular, in workplace lighting a color and / or luminance shading can be perceived as disturbing. To illustrate this, for example, one can assume a cuboid to be illuminated as a shadow casting object, which stands on a flat surface, such as a table or worktop, in the center of the origin of a spatial coordinate system (X, Y, Z) and has a spatial extent of 5 mm in each of the X and Y directions and of 150 mm in Z direction. Direction has what corresponds to the height of the cuboid top over the flat surface. Furthermore, one can assume a lighting device with a red and a green LED, which have a distance of 3 mm to each other for conventional lighting devices and at a height of 1000 mm above the flat surface corresponding to a vertical spatial coordinate Z = 1000 mm and horizontal spatial coordinates X = 500 mm and Y = 500 mm is appropriate. By simulations it can be shown that on the flat surface next to a black core shadow of the cuboid, a colored edge in the form of a color shadow of 0.2 mm width is perceptible, the red LED on one side and the green LED on the other side. Furthermore, assuming an observer observing the shadow from a distance of typically about 0.7 m, the width of the color shadows corresponds to a respective spatial resolution of about 1 arc minute, so that the color shadows are still clearly perceptible even from this distance. In such a workplace lighting, the maximum distance of the differently colored LEDs would have to be less than about 1.5 mm to each other in order to avoid the otherwise clearly visible and discrete discernible color fringes and luminance seams, which is technically usually not possible.

It can also be shown that an additional use of a common reflector for the LEDs of a lighting device does not affect the colored shadows and rather leads to discrete, regular, "rhythmic" color patterns.

Therefore, in conventional LED clusters lighting devices, optical films, such as diffusion films, are commonly used, but which reduce optical efficiency.
In the publication US 2010/0140633 A1 there is described an LED package having a plurality of white, yellow-green and red-emitting LEDs equally spaced in a regular pattern which is rotationally symmetric with respect to the emission colors when rotated by 90 °.
An object of at least one embodiment is to provide a light source with light emitting diodes, which can at least reduce the disadvantages described above. This object is achieved by an object having the features of the independent claim. Advantageous embodiments and further developments of the subject matter are characterized in the dependent claims and will be apparent from the following description and drawing 2.
In particular, a light source according to at least one embodiment of the invention comprises at least one illumination unit with a plurality of light-emitting diodes, which has a plurality of first light-emitting diodes and a plurality of second light-emitting diodes. The first and second light-emitting diodes each radiate light with each other different colors. Furthermore, the plurality of light emitting diodes are arranged along a curved curve.

Here and below, a curved curve denotes a continuous, continuous and gapless curve which, at least in theory, the light emitting diodes (LEDs) with each other combines. Furthermore, the curved curve has no straight sections and no kinks. In other words, always three directly adjacent LEDs of the plurality of LEDs are not arranged along a straight line. In particular, the curved curve may be selected in its basic form from a group formed by a circle, an ellipse, a circular arc, an elliptical arc, a spiral, a spline, and combinations thereof. In this case, a spline is referred to as a curve which has curve pieces set against each other continuously and without kinks, each of which can be defined, for example, by polynomial functions, circular functions, elliptical functions and / or trigonometric functions. A spline can thus also be referred to as a free-form curve, which is continuous and at least one time differentiable especially in the mathematical sense and thus has no gaps or kinks. If the arrangement of the positions of the LEDs in the light source is defined as points in a coordinate system, the curved curve represents in particular that curve which, given given boundary conditions, indicates the shortest curve which connects all points defined by the LEDs. The given boundary conditions may for example be particularly preferably selected from the basic shape of the curved curve and optionally from the maximum degree of polynomial of curved pieces of a spline.

As with conventional lighting fixtures, each of the plurality of LEDs when illuminated illuminates an object with a shadow behind the object corresponding to the color of that LED. The arrangement of the plurality of LEDs along the curved curve in the light source described here, however, differs from conventional arrangements of LEDs in matrix-like patterns with rows and columns, which can be achieved with advantage in the illumination of the object, a superposition of the different shadow throws of the first and second LEDs, whereby the recognizable in known lighting devices with different colored LEDs color shadows and luminance shadows can at least be reduced or even no longer perceptible to a viewer.

In other words, with the light source described here, perceptible colored shadows and in particular "rhythms" and regularities in luminance and color of the shadows, ie color shadows and luminance shadows, can be minimized or even eliminated in comparison to known lighting devices with a plurality of differently colored LEDs, without, for example, one optical film such as a scattering film in the beam path of the light emitting diodes must be arranged. In particular, it may be possible that advantageously the shadows flow out in the perception of a viewer and can blur with respect to light density and color variations and / or can fall under the resolution of the human eye.

A first element and a second element, such as a first LED and a second LED or two first LEDs or two second LEDs are here and below adjacent to each other directly along the curved curve when starting from the first element along the course of the curved Curve to the second element no further first element and no further second element is arranged. A first and second element are otherwise directly adjacent to each other when the distance from the first element to the second element is shorter than the distances of the first element to each further second element.

The above-explained effect of the light source described here, in that color shadows and luminance shadows can be reduced or completely prevented, can be further promoted and enhanced by at least one or more of the following embodiments.

Particularly preferably, the first and second LEDs can be arranged alternately along the curved line. In each case a first and a second light-emitting diode directly adjacent to the curved curve can form a lighting group in the majority of the LEDs. Thus, the first and second LEDs may form a plurality of lighting groups. Between the lighting groups further first and / or second LEDs can be arranged. Each illumination group may have a respective arrangement direction defined by the first to the second light emitting diode. With particular advantage, the respective arrangement directions of at least two lighting groups are different. In other words, at least two of the lighting groups are rotated against each other. In addition, a plurality of lighting groups or even all lighting groups can be rotated against each other and thus have different arrangement directions from each other.

Furthermore, each of the illumination groups may have a spacing between the first and second LEDs, the respective distance being at least two illumination groups, preferably a plurality of illumination groups, and / or particularly preferably is different for all lighting groups.

Furthermore, a distance of at least two first LEDs adjacent to each other along the curved curve may be different from a distance of at least two second LEDs adjacent to one another along the curved curve. Additionally or alternatively, in at least three first and / or second LEDs adjacent to each other along the curved curve, the two distances of the respectively two directly adjacent LEDs may be different. In other words, a first and / or a second LED to two along the curved curve in different directions directly adjacent first and second LEDs have different distances.

Preferably, a plurality of first and / or second LEDs or particularly preferably all first and / or second LEDs have the aforementioned different distances.

Furthermore, the light source can have a plurality of illumination units. Each of the plurality of illumination units, that is, the at least two illumination units, can have one or more of the aforementioned features. In particular, the lighting units may be different from one another, for example with regard to the curved curves with regard to their size, length and / or shape and / or with regard to the arrangement directions and / or the above-defined distances of at least two or preferably a plurality of lighting groups from different lighting units. In particular, at least two of the plurality of lighting units may each be in the manner described above a plurality of light-emitting diodes arranged on each having a curved curve and the curved curves may be different from each other. Alternatively or additionally, a lighting group of a lighting unit and a directly adjacent lighting group of another lighting unit may have different arrangement directions. This preferably applies to a plurality or particularly preferably to all lighting groups of the lighting units.

With a plurality of illumination units, the respective curved curves are particularly preferably defined such that they do not overlap. For example, the curved curves of the plurality of lighting units may be nested circles, ellipses or arcs thereof. Furthermore, the curved curves can also be arranged side by side. In addition, the curved curves may also be circles, ellipses, circular arcs, elliptical arcs or spirals rotated relative to one another, wherein the curved curves may each be the same or different in terms of their shape.

Furthermore, the plurality of LEDs may additionally include a plurality of third LEDs that emit light having a color different from the first and second LEDs. For example, a plurality of lighting groups with a first and a second LED may additionally have a third LED. Particularly preferably, each of the lighting groups can have a first, a second and a third LED.

With regard to the arrangement and / or the distances of the third LEDs in relation to the first and / or second and / or other third LEDs, the above said to the first and second LEDs applies. In this case, a lighting group can have a first arrangement direction from the first to the second LED and a second arrangement direction from the second to the third LED, wherein the first and second arrangement directions are the same as those mentioned above for the arrangement direction.

The LEDs of the plurality of LEDs can be embodied, for example, as LED chips in the form of semiconductor layer sequences based on arsenide, phosphide and / or nitride compound semiconductor material systems or else as corresponding LED chips in a housing, wherein, for example, each of the plurality of LEDs in FIG a separate housing can be arranged. For example, a first and a second LED and / or optionally a third LED may be arranged in a common housing. Furthermore, one or more LEDs may also have a potting and / or one or more wavelength conversion dyes to achieve a desired color location and a desired color temperature of the emitted light. Such LEDs and modifications thereof are known in the art and will not be further elaborated here.

The plurality of LEDs of a lighting unit or of a plurality of lighting units can be arranged on a common carrier, for example a printed circuit board, and / or on a common heat sink and electrically interconnected. A support for a lighting unit may, for example, be shaped in the shape of the curved curve.

The LEDs of the plurality of LEDs may emit light at a constant intensity during operation, or alternatively each emit light with varying intensities. The respective emission directions of the light emitted by each of the plurality of LEDs may be the same or different. Furthermore, the LEDs of the plurality of LEDs can have one or more lenses and / or one or more reflectors, by means of which the respective emission characteristic of the LEDs can be set. Furthermore, for example, a common carrier may also have a reflector and / or one or more lenses, which are arranged downstream of the plurality of LEDs in the emission direction.

In particular, the plurality of LEDs can emit white light, which may be particularly suitable for illumination purposes. For this purpose, the first LEDs, for example, blue and the second LEDs emit yellow light. Furthermore, the first LEDs can also emit, for example, white light and the second LEDs emit colored light, for example red light, for adjusting the color temperature of the light emitted by the light source. If the light source has a plurality of first, second and third LEDs, they may each emit green, blue and red light, respectively. By a relative change in the brightness of the first, second and optionally third LEDs to one another, the color, brightness and color temperature of the light emitted by the light source can be adjustable.

• Figur 1 eine schematische Darstellung einer Lichtquelle. Figur 1 formt kein Teil der Erfindung.
• Figur 2 eine schematische Darstellung einer Lichtquelle gemäß einem weiteren Ausführungsbeispiel.

In a particularly preferred embodiment, the light source has at least two illumination units, each having a plurality of first and second light-emitting diodes, each arranged on a curved curve in the form of an ellipse or a circle, wherein the curved curves are arranged inside each other and a common center and at least one first light-emitting diode of one of the at least two illumination units and a directly adjacent first light-emitting diode of a second of the at least two illumination units with the center are not arranged on a straight line. Furthermore, the illumination units and / or the plurality of LEDs may have one or more of the above-mentioned features.
By the described different directions of arrangement and the different distances within a lighting unit and the arrangement of several, so of at least two lighting units can be achieved with the greatest possible degree of irregularity in the arrangement of the first and second and possibly also the third LEDs with advantage, whereby Farbschatten and / or luminance shadows can be reduced or completely prevented. In comparison to conventional illumination devices, which often have LEDs of one color in large numbers and also other LEDs of a different color in a small number to produce the desired mixed light, a comparatively larger number of differently colored LEDs can be used in the light source described here.
Further advantages and advantageous embodiments and developments of the invention will become apparent from the following in connection with the FIG. 2 described embodiments.
Show it:

• FIG. 1 a schematic representation of a light source. FIG. 1 does not form part of the invention.
• FIG. 2 a schematic representation of a light source according to another embodiment.

In the exemplary embodiments and figures, identical or identically acting components may each be provided with the same reference numerals. The illustrated elements and their proportions with each other are basically not to be regarded as true to scale, but individual elements, such as layers, components, components and areas, for better representation and / or better understanding exaggerated be shown thick or large.

In FIG. 1 (not part of the invention) an embodiment of a light source 100 is shown, which has a lighting unit 10. The lighting unit 10 includes a plurality of light emitting diodes (LEDs) having a plurality of first LEDs 1 and a plurality of second LEDs 2, the first LEDs 1 emitting light having a color different from the second LEDs 2. For example, the first LEDs 1 emit blue light and the second LEDs 2 emit yellow light so that the superposition of the blue and yellow light from the light source 100 results in emitted white light.
The majority of the LEDs, that is to say the majority of the first and second LEDs 1, 2, are arranged along a curved curve 4, which in the exemplary embodiment shown is designed purely by way of example as an elliptical arc. Alternatively, the arcuate curve may be implemented as a circle, ellipse, arc, spiral, spline, or combination thereof, as described in the general part.

The first and second LEDs 1, 2 are arranged alternately along the curved curve 4, wherein a first LED 1 and a second LED 2 adjacent thereto directly along the curved curve 4 form a lighting group 5, 5 ', 5 "between the lighting groups 5, 5 ', 5 ", additional LEDs may additionally be arranged, for example first and / or second LEDs 1, 2 or LEDs different therefrom.

Each illumination group 5, 5 ', 5 "has a respective arrangement direction 6, 6', 6", which points from the respective first LED 1 to the respective second LED 2. The arrangement directions 6, 6 ', 6 "and thus the lighting groups 5, 5', 5" are rotated against each other.

Furthermore, the illumination groups 5, 5 ', 5 "each have different distances from one another, In particular, the first and second LEDs 1 also have different distances to the respective first and second LEDs directly adjacent to the curved curve 4. Furthermore, a distance of at least two directly adjacent to the curved curve 4 directly adjacent first light-emitting diodes 1 different from a distance of at least two directly adjacent second light-emitting diodes. 2

The first and second LEDs 1, 2 thus exhibit a high degree of irregularity as a result of the arrangement shown along the curved curve 4, whereby color shadows and luminance shadows can be reduced when illuminating an object by the light source 100 in comparison to conventional illumination devices with LEDs of different colors ,

The light source 100 furthermore has a common carrier (not shown) for the first and second LEDs 1, 2 designed as semiconductor chips. The carrier has a printed circuit board which is shaped in accordance with the curved curve 4.

In FIG. 2 an embodiment of a light source 200 is shown, which in addition to the first and second LEDs 1, 2 has a plurality of third LEDs 3 compared to the previous embodiment, with only some of the LEDs 1, 2, 3, provided for clarity with reference numerals are. Each illumination group 5, 5 ', 5 "is assigned a first LED 1, a second LED 2 and a third LED 3.
The third LEDs radiate different light from the first and second LEDs 1, 2. In the exemplary embodiment shown, the first LEDs 1 emit blue light, the second LEDs 2 green light and the third LEDs 3 red light, so that the light source 200 emits white light. The intensity radiated by the first, second and third LEDs 1, 2, 3 may be adjustable so that the color temperature and the color location of the light emitted by the light source 200 may be selectable thereby.

In the exemplary embodiment shown, the light source 200 has three illumination units 10, 20, 30, each with the plurality of LEDs, that is, the majority of the first, second, and third LEDs 1, 2, 3. Each plurality of LEDs of the illumination units 10, 20, 30 are arranged on a respective curved curve 4, 4 ', 4 "in the form of an ellipse curved curves, for example, be circles or closed splines.

Each of the lighting units 10, 20, 30 has a printed circuit board extending along the respective curved curve 4, 4 ', 4 ", on which the first, second and third LEDs 1, 2, 3 are respectively mounted and interconnected.

The curved curves 4, 4 ', 4 "are arranged one inside the other and have a common center 9, wherein at least a first light-emitting diode 1 of the illumination group 5' of the illumination unit 10 and a directly adjacent first light-emitting diode 1 of the illumination group 5" of the illumination unit 20 are arranged with the center 9 not on a straight line. In particular, in the exemplary embodiment shown, no first LEDs 1, no second LEDs 2 and no third LEDs 3 with directly adjacent respective same LEDs 1, 2, 3 are arranged with the center 9 on a straight line, so that the lighting groups of the lighting units 10, 20th , 30 are rotated around the center 9 against each other or shifted. As a result, each of the lighting groups of one of the lighting units 10, 20, 30 and the respectively adjacent lighting group of another of the lighting units 10, 20, 30 have different arrangement directions.

Furthermore, in addition, the respective distances from each other along the respective curved curve 4, 4 ', 4 "directly adjacent lighting groups to each other, so that the lighting units 10, 20, 30 with respect to the individual lighting groups unevenly against each other are rotated. The distances between the first LEDs 1 to the second LEDs 2 and the second LEDs 2 to the third LEDs 3 are always approximately the same for the lighting groups in the embodiment shown. Alternatively, the respective distances may also be varied differently and irregularly from lighting group to lighting group.

By arranging the plurality of LEDs 1, 2, 3 along the curved curves 4, 4 ', 4 ", the illumination of an object with the light source 200 causes an overlaying and, in particular, turbulence of the color shadows, which is simulated by simulating an oblique view on one Cuboid with an edge length of each 300 mm irradiated illumination could be shown by means of the light source described here 200. This leads to outflowing shadows and smooth color gradients in the shadows, where discrete color shadows as in conventional lighting devices with different colored LEDs with clearly distinguishable color coordinates, the so-called In particular, the conventionally occurring color differences in the light source 200 are minimized by the swirl, so that no regularity and no rhythm in luminance and / or color of the shadows occurs.

Alternatively or additionally, the light sources 100, 200 may also have further features of the embodiments described in the general part.

The invention is not limited by the description based on the embodiments of these. Rather, the invention encompasses every new feature as well as every combination of features, which in particular any combination of features in includes the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

Claims (11)

1. A light source comprising at least two illumination units (10, 20, 30)

   - having in each case a plurality of light-emitting diodes comprising a plurality of first light-emitting diodes (1) and a plurality of second light-emitting diodes (2),

   - wherein the first and second light-emitting diodes (1, 2) emit light having mutually different colors, and

   - wherein each of the pluralities of the light-emitting diodes is arranged along a bent curve (4, 4', 4") in the form of an ellipse or a circle,

   - wherein in each case one first and one second light-emitting diode (1, 2) that are directly adjacent along the bent curve (4, 4', 4") form an illumination group (5, 5', 5") having a respective arrangement direction (6, 6', 6") from the first to the second light-emitting diode (1, 2),

   - wherein the respective arrangement directions (6, 6', 6") of all illumination groups (5, 5',5") are different,

   characterized in that
   all illumination groups (5, 5', 5") have distances between the respective first and second light-emitting diode (1, 2) which are different,
   wherein the bent curves (4, 4', 4") are arranged one in another and have a common mid point (9), and at least one first light-emitting diode (1) of one of the at least two illumination units (10, 20, 30) and a first light-emitting diode (1), directly adjacent thereto, of a second of the at least two illumination units (10, 20, 30) together with the mid point (9) are not arranged on a straight line.
2. The light source according to any of the preceding claims, wherein a distance between at least two first light-emitting diodes (1) that are directly adjacent along the bent curve (4, 4', 4") is different from a distance between at least two directly adjacent second light-emitting diodes (2).
3. The light source according to any of the preceding claims, wherein the distances between at least three first light-emitting diodes (1) that are directly adjacent to one another along the bent curve (4, 4', 4") are different in each case.
4. The light source according to any of the preceding claims, wherein the distances between at least three second light-emitting diodes (2) that are directly adjacent to one another along the bent curve (4, 4', 4") are different in each case.
5. The light source according to any of the preceding claims, comprising a plurality of illumination units (10, 20, 30) that differ from one another.
6. The light source according to the preceding claim, wherein the illumination units (10, 20, 30) in each case have a plurality of light-emitting diodes arranged along a respective bent curve (4, 4', 4") and the bent curves (4, 4', 4") differ from one another.
7. The light source according to claim 5 or 6, wherein the bent curves (4, 4', 4") of the plurality of the illumination units (10, 20, 30) do not overlap.
8. The light source according to any of claims 5 to 7, wherein at least one illumination group (5') of one illumination unit (10) and an illumination group (5"), directly adjacent thereto, of another illumination unit (20) have different arrangement directions.
9. The light source according to any of the preceding claims, wherein the plurality of light-emitting diodes furthermore has a plurality of third light-emitting diodes (3), which emits light having a different color than the first and second light-emitting diodes (1, 2).
10. The light source according to any of the preceding claims, wherein each of the illumination groups (5, 5', 5") has a first, a second and a third light-emitting diode (1, 2, 3).
11. The light source according to any of the preceding claims, wherein the plurality of the light-emitting diodes of the at least one illumination unit (10, 20, 30) emits white light.

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