Patent Application
20190277476
The invention relates to the field of lighting, and more specifically to a lighting assembly.
LEDs are used today for an increasing number of lighting applications due to advantageous properties such as high energy efficiency, compact size and long lifetime. However, while many lighting applications require light output to be spread over a larger area, the light output from LEDs is rather concentrated to small areas. If a plurality of LEDs is used, these are generally arranged at a certain distance from each other due to thermal limitations and for cost reasons.
In order to obtain a relatively homogeneous light output from a plurality of LEDs, it is generally known to position a diffusor element in front of the LEDs. However, the arrangement of individual LEDs behind the diffusor is still visible in many cases, such that the light output over the front surface of the diffusor is not very homogeneous, leading to a spotty appearance. While a very thick diffusor may achieve better homogeneity, this will lead to reduced overall efficiency.
JP 2013 196847 A discloses an LED lamp with LEDs provided at a substrate in a glass tube. A diffusion reflection part is formed on the circumference of the glass tube. The width of the diffusion reflection part in circumference direction varies throughout the longitudinal direction of the glass tube.
EP 1 028 348 A1 discloses an arrangement for producing a uniform illumination from a light source, for a surface to be illuminated, comprising a light source located behind a screen. The screen thickness varies over the surface cross section.
WO 2008/025909 A1 discloses an optical system comprising a diffuser for a homogenized luminance output.
It could be considered an object to provide a lighting assembly for achieving a more homogeneous appearance, in particular with a compact arrangement.
This is achieved by the lighting assembly according to claim 1. Dependent claims refer to preferred embodiments.
According to the invention, at least two LED lighting elements are provided. The term “LED lighting elements” should be understood to cover any known type of solid state lighting element, such as e.g. light emitting diodes, organic light emitting diodes, laser diodes, etc. Each LED lighting element may comprise one or a plurality of such components arranged in proximity. For example, one LED lighting element may comprise two or more dies of light emitting diodes. In particular, it is possible to provide light emitting diodes of different color placed in proximity, such as e.g. in an RGB LED. The LED lighting elements may be individually packaged components, i.e. they may comprise individual housings with electrical terminals. Also, it is possible to provide the LED lighting elements as pure unpackaged LED dies, e.g. connected directly to a leadframe.
The lighting assembly comprises at least two LED lighting elements, but a larger number is preferred, such as at least 3, 4 or 5, further preferably e.g. more than 10. The LED lighting elements are arranged at a distance from each other. While this is not required, a plurality of LED elements may be equally spaced. In particular, a plurality of LED lighting elements may be arranged in a line, e.g. equidistant according to a constant pitch.
The lighting assembly according to the invention further comprises a diffusor element extending over the LED lighting elements, i.e. being arranged such that light therefrom is emitted into the direction of the diffusor element. The diffusor element is translucent but not entirely transparent, i.e. light traversing the diffusor element is scattered. For example, the diffusor element may comprise diffusion particles embedded in a transparent or translucent material, such as, for example, TiO2 particles dispersed in transparent.
The inventors have considered that the light input from two or more LED lighting elements arranged at a distance from each other is inhomogeneous. Thus, in order to achieve a more homogeneous output from a top surface of the diffusor element, the optical properties of the diffusor element could be chosen non-homogeneous in order to counteract and compensate for the non-homogeneous light input. By a suitable choice of non-homogeneous optical properties of the diffusor element, light output may thus be homogenized.
Accordingly, the diffusor element may be comprised of different diffusion portions providing different levels of optical diffusion in different locations. In the most basic configuration, at least two types of diffusion portions may be provided with different levels of diffusion. First diffusion portions may be arranged in front of the LED lighting elements, and at least one second diffusion portion may be arranged in between the first diffusion portions. The first diffusion portions are disposed to cause stronger optical diffusion than the second diffusion portion.
Embodiments of a lighting assembly including such a non-homogeneous diffusor element with first and second diffusion portions have proven to provide a significantly homogenized light output as compared to a homogeneous diffusor element. A definition of the most preferred, fully homogeneous appearance would be a lambertian type emission of light from the surface with fully uniform luminance, i.e. no spatial variation. For practical embodiments of a light emitting surface, a homogeneity value may be defined as the standard deviation of the luminance values over the surface area divided by the mean luminance value over the surface area. Homogeneity values of e.g. 50%, preferably 40% or less may be regarded satisfactory for some applications. Values of 25% or less are preferred; especially preferred are values of 10% or less, which are generally perceived as fully homogeneous.
In particular, satisfactory homogeneity values were obtained with the current invention already with a relatively thin diffusor element, thus maintaining high efficiency.
The lighting assembly according to the invention is especially suited to provide line-shaped illumination, in particular in very compact assemblies. A plurality, or all, of the LED lighting elements may be arranged in a line. One or more diffusor elements may be provided to cover the LED lighting elements, being arranged such that first diffusion portions are each positioned in front of the LED lighting elements. Consequently, second diffusion portions may be arranged in between the LED lighting elements.
While in principle an improvement in the homogeneity of the light output may be achieved with a stepwise variation of the level of optical diffusion changing between the first and second diffusion portions (with optionally intermediate portions in between), this is not preferred since steps may be visible in the luminance appearance. Therefore, it is generally preferred to provide a diffusor element where the level of optical diffusion varies continuously between the first and second diffusion portions. Preferably, the level of optical diffusion decreases monotonously from the first diffusion portions to the second diffusion portions.
According to one embodiment, the diffusor element comprises diffusion particles embedded in a transparent or translucent material. In order to achieve the different levels of optical diffusion in the first and second diffusion portions (as well as optionally in any intermediate portions), the density of the diffusion particles may vary. The density in the first diffusion portions arranged in front of the LED lighting elements may be higher than the density in the second diffusion portions arranged in between the LED lighting elements.
In a preferred embodiment, the different levels of optical diffusion in the first and second diffusion portions (as well as optionally any intermediate portions arranged in between the first and second diffusion portions) may be achieved by varying the thickness of the diffusor element. The thickness may e.g. be measured perpendicularly to a line or plane in which the LEDs are arranged. The first diffusion portions may be provided with a higher thickness than the second diffusion portions, such that light traversing the diffusor element at the first diffusion portions propagates a longer distance through the diffusor element in the first diffusion portions, thus undergoing stronger diffusion.
A diffusor element of varying thickness may have a constant density of diffusion particles, which is easier to manufacture. However, it is also possible to combine a variation in particle density and a variation in thickness.
Particularly in arrangements of LED elements along a line, the level of optical diffusion of an elongate diffusor element may vary along its length. If the LED elements are arranged at equal distances according to a first pitch, it is advantageous to provide a variation in the level of optical diffusion to be equally periodical with a second pitch equal to the first pitch. For example, the thickness of the diffusor element may vary periodically with the same pitch as the arrangement of the LED lighting elements, and preferably the arrangement of the LED lighting elements and of the thickness are spatially in phase, such that the maxima of the thickness are arranged directly above the LED lighting elements.
In a preferred embodiment, a top surface of the diffusor element may have a plane shape. An opposed bottom surface oriented towards the LED lighting elements may have an undulating shape to obtain varying thickness.
The variation of the thickness of the diffusor element may e.g. be such that first diffusion portions, e.g. corresponding to the maximum thickness, are at least 50% thicker than second diffusion portions, e.g. corresponding to the minimum thickness of the diffusor element. Further preferred, the first diffusion portions are at least 100% thicker than the second diffusion portions.
In preferred embodiments, the LED lighting elements may be arranged with electrical conductors extending between them. In particular, a leadframe may connect the LED lighting elements.
It is further preferred to provide a housing at least partly surrounding the LED lighting elements and the diffusor. The housing may comprise reflective surfaces to improve efficiency. In particular, at least the inner surfaces of the housing oriented towards the LED lighting elements may be reflective. It is particularly preferred for a housing to cover the lateral and bottom surfaces of the lighting assembly, but not the top surface of the diffusor. The housing may be made of a flexible material, e.g. silicone.
The lighting assembly according to the invention is particularly suited to be manufactured with very compact dimensions. For example, the height, e.g. measured from the bottom surface of the lighting assembly to a light emitting top surface of the diffusor may be less than 1 cm, further preferably equal to or less than 8 mm, particularly preferably 5 mm or less. Compared to the pitch of the LED elements, the height may be less than the pitch, preferably correspond to 50% or less of the pitch of the LED elements.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings,
An elongate lighting assembly 10 is shown in
The lighting assembly 10 is of particularly small dimensions, in a preferred example with a height measured from the bottom surface 12 to the top surface 14 of only 4 mm and a width of only 7 mm.
The length in a longitudinal direction L may vary, but will be significantly greater than the width, e.g. at least 10 times greater.
In the interior of the lighting assembly 10, as shown in the cross-section of
If supplied with electrical operating power, the LEDs 20 are disposed to emit light into the direction of the top surface 14, as schematically shown in dotted lines in
The LEDs 20 and the diffusor 30 are enclosed by a housing 28, covering the lateral sides and the bottom of the lighting assembly 10. The inner surfaces of the housing 28 are reflective. The space between the LEDs 20 and the diffusor 30 is filled with a transparent light guide 32, which may be made from silicone.
As shown in
Between the maxima and the minima, the thickness d varies continuously in the example shown. For example, the variation may be according to a sine function.
Due to the varying thickness of the diffusor 30, the first diffusion portions 30a cause a stronger diffusion effect than the thinner second diffusion portions 30b. Since the first diffusion portions 30a are arranged directly in front of the light emitting portions of the LEDs 20, the light 34a emitted therefrom perpendicular to the plane of the LEDs 20 is strongly diffused, whereas light 34b emitted under greater angles towards the second diffusion portions 30b undergoes a lower degree of diffusion. Overall, this leads to relatively homogeneous emission of light from the front surface 14a of the diffusor 30, i.e. to a uniform luminance.
In specific embodiments, the choice of the exact mathematical function of the thickness variation as well as the choice of dimension parameters d0, d1, and l may depend on the spread of the light emitted from the LEDs 20 as well as the distance between the LEDs 20 and the diffusor 30. The parameters may, for each application, be chosen to obtain the desired homogeneity value.
Since the level of diffusion caused by the denser diffusion particles in the first diffusion portions 30a is stronger than in the second diffusion portions 30b, this achieves the same effect of homogenizing the light output as described above.
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.
For example, while the above embodiments show a constant pitch both for the variations in the diffusor 30 and the placement of the LEDs 20, the arrangement need not in all cases be equidistant, as long as the first diffusion portions 30a are arranged in front of the LEDs 20. While the LEDs 20 shown in the above examples are packaged LEDs, it is also possible to use unpackaged LED dies.
Other variations to the disclosed embodiment can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims.
In the claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality.
The mere fact that certain measures are recited in mutually different dependent claims or embodiments does not indicate that a combination of these measures cannot be used to advantage. For example, it is possible to combine a variation in thickness with a variation in the density of diffusion particles.
Any reference signs in the claims should not be construed as limiting the scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16191317.3 | Sep 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/073322 | 9/15/2017 | WO | 00 |
