DE102010030938A1 - Light box and method for mixing light - Google Patents

Abstract

A light box (1) has a housing (2, 3, 4) with a light exit opening, at least one semiconductor light source (5) being accommodated in the housing 2, 3, 4), at least one semiconductor light source (5) at least partially on an inside (6) a wall (4) of the housing (2, 3, 4) radiates, the inside (6) is at least partially covered with at least one phosphor (7; 12; 13), the light outlet opening is covered by a translucent cover (3) and the cover (3) is a light-scattering, fluorescent-free cover (3).

Description

The invention relates to a light box (also called 'light box'), wherein the light box has a housing with a light exit opening in the housing at least one semiconductor light source, in particular light emitting diode is housed, the at least partially radiates at least one semiconductor light source on an inner side of a wall of the housing , the inside is at least partially covered with at least one phosphor and the light exit opening is covered by a translucent cover. The invention further relates to a method for mixing light.

When producing white mixed light of light of blue LEDs and LED-near phosphor (which partially converts the blue light of the LEDs in yellow or yellow-green light ("blue-yellow conversion"), in addition to a heating of the phosphor by a Heat evolution at the LEDs Heat due to Stokes loss during light conversion, which can result in loss of efficiency in conversion and degradation of the phosphor above about 100 ° C to 150 ° C.

In addition, the phosphor partly emits the wavelength-converted or converted light back to the LEDs, which leads to a strong absorption of the converted light in the LEDs when the phosphor is applied close to the LED.

The meeting of the desired target color location of the mixed light depends on a passage through a phosphor layer (transmission) of a concentration of the phosphor and a layer thickness, which leads to manufacturing fluctuations in the color location and the problem of so-called "Binnings" (a necessary sorting of the light sources after their actual color location).

To reduce the heating of the phosphor by the waste heat of LEDs, this can be located away from the LEDs ("remote phosphor"), wherein the phosphor is still used in transmission. For this purpose, a use of a relatively large light box is known. The light box has a housing with a light exit opening, wherein in the housing at least one LED is housed, which at least partially radiates on an inner side of a wall of the housing. The inside is highly reflective designed to geometrically reduce back reflections on the LEDs. The light exit opening has the phosphor. In this case, however, the phosphor still warms up strongly, which limits the achievable luminous flux. In addition, binning is still problematic. A further disadvantage is that the light exit surface in the off state appears garish yellow due to the dye.

It is also known a lightbox whose inside is not highly reflective, but is covered with a phosphor. Thus, phosphor is present both on the light exit surface, as well as on the inside of the housing. In this variant of the light box, the phosphor still heats up strongly, and the light exit surface also appears yellow in the off state, which is also disadvantageous from a design point of view.

It is the object of the present invention to at least reduce the disadvantages of the prior art, and in particular to provide a light box which allows little heating of the phosphor, which has an improved appearance and which shows good color mixing.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a light box, comprising a housing with a light exit opening, wherein at least one semiconductor light source is housed in the housing, at least one semiconductor light source at least partially radiates on an inner side of a wall of the housing, the inner side is at least partially covered with at least one phosphor, the light exit opening is covered by (and is formed by) a translucent cover and the cover is a light diffusing, phosphor-free cover. It is particularly advantageous if the cover extends almost completely between the side walls, d. H. in the plane of the cover practically no light-impermeable housing parts of the light box are arranged.

The phosphor on the housing can be efficiently cooled since the housing can be connected directly to a heat sink and / or can itself act as a heat sink. The comparatively poorly coolable phosphor in the cover is omitted here. Therefore, even high luminous fluxes of more than 3000 lumens are possible without any problems. Due to the absence of the phosphor in the cover and also due to the light-scattering property, it no longer appears yellow. Due to the scattering effect of the cover also an improved color and location homogenization of the exiting luminous flux can be achieved. Furthermore, the housing and thus the light box are particularly compact or small ausgestaltbar what, among other things, a light guide through a downstream optics, z. As a lens facilitated.

It is an embodiment that an outer side of the housing (in particular on a region facing away from the at least one phosphor) is thermally connected to a heat sink or a housing, in particular a lamp or lamp, and / or on its outside with a cooling structure (cooling fins, cooling pins or other cooling projections) is provided. As a result, the phosphor can be cooled particularly effectively.

The cover may be any suitable light-diffusing and translucent material, e.g. B. diffused glass (eg., Frosted glass) or a diffusely scattering plastic. The cover can also be considered as a primary optic and allow (other) light shaping in addition to the light scattering function. The cover can z. B. at the same time be configured as a lens.

It is still an embodiment that the inside of the housing is at least partially covered with at least one Inertstreumaterial, d. h., With a material which for the non-wavelength-converted (originally emitted by the at least one semiconductor light source) light and / or wavelength-converted light acts as a scattering material and does not itself act as a phosphor. As a result, a scattering of light incident on the inner wall of the light box, in particular also light which has not been converted to wavelength (for example, blue), can be set so that a desired color location of the mixed light is better hit. The inert material and the phosphor can be mixed and applied in a same layer on the inner wall.

It is yet another embodiment that the housing has a cylindrical basic shape, which improves a directionally homogeneous light emission. Alternatively, but also different shaped housing are possible, for. B. with a cuboid basic shape.

In particular, for the precise setting of a desired color location, z. As a white mixed light, in particular by means of a partial blue-yellow conversion, it may be a development that the directly striking the cover portion of the emitted light from the at least one semiconductor light source in about the required for setting the desired color location light component unconverted light equivalent. As a result, in particular a comparatively erroneous adjustment of a wavelength conversion degree of the phosphor on the inside can be dispensed with, for example, By selecting the wavelength conversion degree of the phosphor (eg, by adjusting the phosphor density and / or the layer thickness) such that virtually full conversion (of nearly 100%) takes place on the inside. A color location of the light box may then be achieved in particular only by the geometric shape of the light box (basic shape, dimensions, etc.), possibly taking into account a radiation characteristic of the semiconductor light source (s).

In particular, for a white mixed light generated from a blue-yellow conversion, a proportion of the blue light on the white mixed light is about 25%. From this, in particular with a Lambert radiation characteristic of the at least one semiconductor light source to a preferred height h of the housing of at least tan (30 °) × radius r of the housing, ie h ~ 2 · r, be closed for directly incident on the cover blue light. It is a preferred development that a height of the housing corresponds at least approximately to twice the radius of the housing (in particular in the case of a cylindrical basic shape, otherwise eg an edge length or a length of a surface bisector of a cover surface). For example, with a lower degree of conversion or conversion of the phosphor, the light box may have a greater height h.

It is generally a configuration that a light emitted by the at least one semiconductor light source onto the inside of the wall of the housing is for the most part wavelength-converted. This can be done layer thickness independent in particular from a certain layer thickness. As a result, in particular a proportion of the wavelength-converted light to the proportion of the non-wavelength-converted light to the cover element can be set particularly precisely. In particular, a majority can be understood to mean a proportion of at least 90%, in particular a full conversion with virtually complete wavelength conversion or conversion.

It is an embodiment that is advantageous for achieving a particularly high degree of conversion that the at least one semiconductor light source has a main emission direction directed toward the inner wall ('broadly emitting semiconductor light source'). The at least one semiconductor light source may generally have at least one semiconductor light source which has a stronger lateral (or deviating from an optical axis) luminous flux or intensity than a Lambertian radiator. This assists in the occurrence of multiple reflections on the inner wall of the housing, which in turn increases the degree of conversion. Also, the housing can then be configured lower (with a lower height h).

An example of a broadly emitting semiconductor light source are the LEDs provided with a primary optics of the "Golden Dragon Argus" line. the company Osram. It may therefore be an advantageous development that the at least one semiconductor light source comprises at least one wide-emitting light emitting diode.

It is an advantageous embodiment for increasing a luminous efficacy and a wavelength conversion degree that the inside of the wall has a highly reflective surface on which the at least one phosphor is applied. As a result, light passing through the phosphor layer or light radiated toward the inside by the phosphor is substantially completely reflected back into the interior of the housing. This embodiment is particularly advantageous for thin phosphor layers, in particular those in which no full conversion occurs without the reflective surface, with the reflective surface, however, already. The highly reflective surface may be formed by means of a reflective layer (which, for example, may be part of a reflective layer system), in particular a miro-layer or a miro-layer system, e.g. B. 'Miro' or 'Miro Silver' Fa. Alanod, or another highly reflective coated wall, in particular made of aluminum.

The at least one phosphor may comprise one or more different phosphors (eg, converting into different wavelengths and / or sensitive to different wavelengths), i. H. the concept of the at least one phosphor also expressly implies the use of more than one phosphor. The use of different phosphors even facilitates or even allows a setting of certain color locations, eg. B. of warm white colors.

Different phosphors can z. B. be mixed (phosphor mixture). However, it is an advantageous embodiment for a lower mutual influence of the phosphors, that the inside of the wall is covered with a plurality of differently positioned phosphor areas with at least two different phosphors. In other words, a geometrically separate application of multiple phosphors is possible. The inner wall is advantageously completely covered with the phosphors. This is also advantageous for only one phosphor. The different phosphor regions thus advantageously adjoin one another directly.

It is advantageous for a simple application of the phosphors, in particular in a full-coverage arrangement, advantageous embodiment that the phosphor regions are arranged in strips. The stripes can be vertical or horizontal. A possible angular or directional color inhomogeneity can be leveled by narrower stripes and / or the scattering effect of the cover.

It is also an embodiment that the at least one semiconductor light source comprises a blue-emitting light source and at least one phosphor can convert blue light into yellowish (yellow or yellow-green) light. However, it is also different colored light sources and phosphors used.

The at least one semiconductor light source may generally comprise at least one light-emitting diode. The light emitted by the at least one light emitting diode may be a visible light, an infrared light (IR LED) or an ultraviolet light (UV LED). The at least one light-emitting diode can be in the form of at least one individually housed light-emitting diode or in the form of at least one LED chip. Several LED chips can be mounted on a common substrate ("submount"). The at least one light emitting diode may be equipped with at least one own and / or common optics for beam guidance, z. At least one Fresnel lens, collimator and so on. Instead of or in addition to inorganic light emitting diodes, z. Based on InGaN or AlInGaP, organic LEDs (OLEDs, eg polymer OLEDs) can generally also be used. Alternatively, the at least one semiconductor light source z. B. have at least one diode laser.

In general, in the presence of a plurality of semiconductor light sources, in particular light-emitting diodes, they can shine in the same color or in different colors.

If different colored semiconductor light sources are present in the housing, at least one phosphor can be sensitive or active with respect to some or all of the colors. Alternatively, the light box on different phosphors for different colored semiconductor light sources.

It is a further development that at least one phosphor is provided for semiconductor light source (s) of a first color and no phosphor is provided for semiconductor light source (s) of a second color. In other words, the lighting device may have at least one semiconductor light source to which no phosphor is assigned.

The light of the semiconductor light sources 1) of the first color is thus at least partially converted to another color while the light of the semiconductor light source (s) of the second color is not converted. This development allows a particularly simple setting of the desired color location.

In particular, the at least one semiconductor light source to which no phosphor is assigned can comprise at least one red-emitting semiconductor light source. As a result, in particular in the case of a blue-yellow conversion, in which the phosphor converts blue light into a yellow-green light, the color locus can be shifted towards white or warm-white without it (as in the case of additional use, for example) a blue in red converting phosphor) to light losses occurs. The light box thus has at least one blue semiconductor light source and at least one red semiconductor light source, as well as a phosphor which reacts to the blue light emitted by the blue semiconductor light source but not to the red light emitted by the red semiconductor light source. Thus, blue primary light, yellow-green conversion light and red primary light are mixed at the cover or light exit surface, so that overall a white, in particular warm white, mixed light results. However, it is also possible, for example, to use at least one blue semiconductor light source with a blue phosphor converting into yellow or yellow-green light and with a blue phosphor converting into red light, wherein the phosphors can be arranged in particular spatially separated.

It is still an embodiment that the phosphor-carrying wall of the housing comprises aluminum or a bent sheet metal. As a result, a good heat-conducting wall is provided at a comparatively low cost and with a low weight.

• – (Insbesondere anteiliges) Aussenden von Licht mindestens einer Halbleiterlichtquelle auf mindestens einen Leuchtstoff an einer Innenwand eines Lichtkastens, wobei zumindest ein von dem Leuchtstoff wellenlängenumgewandeltes Licht auf eine lichtdurchlässige lichtstreuende und leuchtstofffreie Abdeckung fällt (dabei kann es eine Variante sein, dass ein Teil des auf den Leuchtstoff auftreffenden Lichts nicht wellenlängenumgewandelt wird);
• – Aussenden von Licht mindestens einer Halbleiterlichtquelle (z. B. auch einer Halbleiterlichtquelle, der kein Leuchtstoff zugeordnet ist) direkt auf die Abdeckung, so dass an der Abdeckung wellenlängenumgewandeltes Licht und das von mindestens einer Halbleiterlichtquelle direkt auf die Abdeckung abgestrahlte Licht mittels der Abdeckung gemischt werden (wobei die Abdeckung selbst keine Wellenlängenumwandlung vornimmt).

The object is also achieved by a method for mixing light, the method having at least the following steps:

• - (In particular proportionate) emitting light from at least one semiconductor light source to at least one phosphor on an inner wall of a light box, wherein at least one of the phosphor wavelength converted light falls on a translucent light-scattering and phosphor-free cover (it may be a variant that a part of on the phosphor incident light is not wavelength converted);
• - Sending light from at least one semiconductor light source (eg., Also a semiconductor light source, which is not assigned to phosphor) directly on the cover, so that at the cover wavelength-converted light and the at least one semiconductor light source directly emitted to the cover light mixed by means of the cover (the cover itself does not perform wavelength conversion).

The method gives the same advantages as the light box and can also be configured analog.

In the following figures, the invention will be described schematically with reference to exemplary embodiments. In this case, the same or equivalent elements may be provided with the same reference numerals for clarity.

1 shows in oblique view from the side a light box;

2 shows in oblique view laterally a laterally open light box according to a first embodiment;

3 Fig. 12 is a plot of a reflectance against a layer thickness of a phosphor for a blue-to-yellow converting phosphor;

3 shows in oblique view laterally a laterally open light box according to a second embodiment; and

4 shows in oblique view laterally a laterally open light box according to a third embodiment.

1 shows in diagonal view from the side a light box 1 , 2 shows the light box 1 open at the side. The light box 1 has a cylinder-like basic shape with a lower cover side 2 , an upper deck side serving as a translucent cover 3 serves, and serving as a side wall circumferential surface 4 on which the case 2 . 3 . 4 form. The lower cover side 2 serves as a support for at least one semiconductor light source in the form of light-emitting diodes 5 , The carrier may, for. As a circuit board or a submount. On an inside 6 the lateral surface 4 is everywhere a fluorescent material 7 applied. The cover 3 is translucent, light-scattering and fluorescent-free.

From the light-emitting diodes 5 emitted light hits partly directly on the cover 3 on and partly on the inside 6 , On the inside 6 can that be from the light emitting diodes 5 radiated light be completely or partially converted into a wavelength-converted light and radiated again, ultimately (lossy) also to the cover 3 , At the cover 3 is thus light of the original color (the light-emitting diodes 5 ) are mixed with the wavelength-converted light and emitted to the outside. By doing that the cover 3 itself contains no phosphor or is occupied, the cover is not heated by Stokes losses in the wavelength conversion. A heat on the phosphor 7 can have an outside 8th the lateral surface are removed. The outside 8th can serve as a cooling surface and optionally have a Kühlstrukur and / or be connected to a heat sink (o. Fig.). Consequently, there is no decrease in the conversion efficiency or degradation of the phosphor here.

By a thickness and / or a concentration of the layered on the inside 6 applied phosphor 7 For example, a degree of conversion (proportion of wave-converted light to non-wavelength-converted light for the phosphor 7 incident light). In addition shows 3 a plot of a reflectance R in% against a layer thickness d of the phosphor 7 in μm between 10 μm and 200 μm for a blue-yellow-converting phosphor 7 in a concentration of 50%. The inside 6 is highly reflective with a reflectance of 95% designed so that it has little absorbent.

Curve K1 shows by way of example the reflection of blue (remitted) light of a blue (blue color emitting) light-emitting diode with a Lambert-like radiation characteristic on the phosphor 7 , So from to the phosphor layer 7 incident blue light that has been reflected ("remitted") again without wavelength conversion. Curve K2 shows the reflection of wavelength-converted light of the blue light-emitting diode with a Lambert-like radiation characteristic on the phosphor 7 , So from to the phosphor layer 7 impinging blue light that has been wavelength converted and re-irradiated. Due to the Stokes losses of about 25% of the energy, which is converted into heat, the two curves K1, K2, which each relate to the energy of the incident light, do not add up to 100%, but only to approx. 75%.

The curves K1 and K2 show that with greater layer thickness d, the degree of conversion (expressed here by the ratio of the reflection of the wavelength-converted light to the reflection of the non-wavelength-converted light) of the phosphor 7 increases until, starting at a layer thickness d of about 100 μm, the degree of conversion remains substantially constant. Thus, in order to be able to set the maximum degree of conversion for the present configuration safely, only the layer thickness d needs to be set so large that it remains above the necessary minimum layer thickness, taking into account usual manufacturing tolerances. The degree of conversion can be z. B. by increasing the concentration of the phosphor further. Likewise, the remission of blue light can be increased in a defined manner by addition of inert spreaders (eg granules of glass or undoped garnet). Thus, the color location of the converted light can be adjusted purely by the chemical-physical composition of the phosphor, but regardless of the layer thickness.

The curves K3 and K4 show analogous dependencies to the curves K1 and K2, but now for light-emitting diodes in the form of a broad-emitting light-emitting diode, which emits a greater proportion of their light onto the phosphor 7 radiates and to have a laterally more pronounced emission, z. B. a light emitting diode of the type "Golden Dragon Argus" from. Osram. At least from a layer thickness d of about 30 microns, the degree of conversion is higher than lambertsch radiating LEDs. Also, an occurrence of multiple reflections is enhanced.

Now again 1 and 2 can at a full conversion, when on the phosphor 7 incident primary (here: blue) light almost completely (here: in yellow or yellow-green light) wavelength is converted, the color location of the mixed light particularly easy by a height h of the lateral surface 4 (More precisely: the vertical distance between an emitting surface of the LEDs 5 and the cover 3 ). For this purpose, the proportion of directly from the LEDs 5 on the cover 3 radiating light so that it corresponds to the desired proportion of the mixed light. With known radiation characteristic of the light-emitting diode (s) 5 Thus, the height h can be determined accordingly. In the case of a Lambertian radiator, for example, this height h is approximately twice that of a radius r (attached to the longitudinal axis L) of the lower cover side 2 , Especially in an assumption of a wide-area arrangement of the LEDs.

The light-emitting diodes can have at least one light-emitting diode, which is not a phosphor 7 is assigned, whose light is thus through the phosphor 7 not converted to wavelengths. The light of such a light-emitting diode (for example at least one red light-emitting diode) can be used in particular for shifting the color locus of the mixed light originating from the conversion.

4 shows in view of obliquely laterally laterally open light box 11 according to a second embodiment. The light box 11 resembles the light box 1 except that now two different phosphors 12 . 13 are present, which spatially separated in vertically aligned stripes 14 . 15 are arranged, with the different stripes 14 . 15 are arranged alternately. This can be a mutual influence of the phosphors 12 . 13 be substantially prevented. The cover 3 can suppress an angle-dependent color inhomogenization. For this purpose, a width of the strips can be reduced.

The phosphors 12 . 13 can respond to the same light emitting diodes or LEDs of different colors. For example, the LEDs may be blue LEDs, and the two phosphors 12 . 13 can convert blue light to yellow-green light (eg, phosphor 12 ) or in red light (eg phosphor 13 ). This can be taken in particular a warm white color. A ratio of the degree of conversion of the two phosphors 12 . 13 with respect to the mixed light, for example, a concentration, thickness and / or width or width ratio of the strips 12 . 13 be set. Alternatively, light emitting diodes of different colors may be used, to which a respective phosphor is assigned, which converts only light of one type of light emitting diode.

5 shows in view of obliquely laterally laterally open light box 21 according to a second embodiment. The light box 11 resembles the light box 21 except that the different phosphors 12 . 13 now in horizontal stripes 22 . 23 are arranged.

Of course, the present invention is not limited to the embodiment shown.

LIST OF REFERENCE NUMBERS

1

light box

2

lower cover page

3

cover

4

lateral surface

5

led

6

Inside of the lateral surface

7

fluorescent

8th

Outside of the lateral surface

11

light box

12

fluorescent

13

fluorescent

14

strip

15

strip

21

light box

22

strip

23

strip

d

layer thickness

H

height

K

Curve

L

longitudinal axis

r

radius

R

reflectivity

Claims (14)

Light box ( 1 ; 11 ; 21 ), comprising a housing ( 2 . 3 . 4 ) with a light exit opening, wherein - in the housing ( 2 . 3 . 4 ) at least one semiconductor light source ( 5 ), - at least one semiconductor light source ( 5 ) at least partially on an inner side ( 6 ) a wall ( 4 ) of the housing ( 2 . 3 . 4 ), - the inside ( 6 ) at least partially with at least one phosphor ( 7 ), - the light exit opening of a translucent cover ( 3 ) and - the cover ( 3 ) a light-scattering, phosphor-free cover ( 3 ). Light box ( 1 ; 11 ; 21 ) according to claim 1, wherein an outside ( 8th ) of the housing ( 2 . 3 . 4 ) is thermally connected to a heat sink. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the inside ( 6 ) the Wall ( 4 ) of the housing ( 2 . 3 . 4 ) is at least partially occupied by at least one inert scattering material. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the housing ( 2 . 3 . 4 ,) has a cylindrical basic shape, wherein a height (h) of the housing ( 2 . 3 . 4 ) equals at least about twice its radius (r). Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein one of the at least one semiconductor light source ( 5 ) on the inside ( 6 ) the Wall ( 4 ) of the housing ( 2 . 3 . 4 ) radiated light is for the most part wavelength converted. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the at least one semiconductor light source ( 5 ) one on the inside ( 6 ) the Wall ( 4 ) directed Hauptabstrahlrichtung. Light box ( 1 ; 11 ; 21 ) according to claim 6, wherein the at least one semiconductor light source ( 5 ) comprises at least one wide-emitting light-emitting diode. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the inside ( 6 ) the Wall ( 4 ) with a plurality of differently positioned phosphor regions ( 14 . 15 ; 22 . 23 ) with at least two different phosphors ( 12 . 13 ) is occupied. Light box ( 1 ; 11 ; 21 ) according to claim 8, wherein the phosphor areas ( 14 . 15 ; 22 . 23 ) are arranged in strips. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the inside ( 6 ) the Wall ( 4 ) has a highly reflective surface on which the at least one phosphor ( 7 ; 12 ; 13 ) is applied. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the at least one semiconductor light source ( 5 ) a blue glowing Has light source and the at least one phosphor ( 7 ; 12 ; 13 ) can convert blue light into yellowish light. Light box ( 1 ; 11 ; 21 ) according to one of the preceding claims, wherein the light box ( 1 ; 11 ; 21 ) at least one semiconductor light source ( 5 ), to which no phosphor is assigned. Light box ( 1 ; 11 ; 21 ) according to any one of the preceding claims, wherein the phosphor ( 7 ; 12 ; 13 ) supporting wall ( 4 ) of the housing ( 2 . 3 . 4 ) Aluminum or a drawn sheet metal. Method for mixing light, the method comprising the following steps: emitting light from at least one semiconductor light source ( 5 ) to at least one phosphor ( 7 ; 12 ; 13 ) on an inner wall ( 6 ) of a light box ( 1 ; 11 ; 21 ), wherein at least one of the at least one phosphor ( 7 ; 12 ; 13 ) wavelength-converted light onto a translucent, light-scattering and phosphor-free cover ( 3 ) falls; Emitting light from at least one semiconductor light source ( 5 ) directly on the cover, so that on the cover ( 3 ) wavelength-converted light and that of at least one semiconductor light source ( 5 ) directly on the cover ( 3 ) radiated light by means of the cover ( 3 ) are mixed.

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