EP3825604A1

EP3825604A1 - Light emitting assembly

Info

Publication number: EP3825604A1
Application number: EP19211121.9A
Authority: EP
Inventors: Dominik Allgaier; Angelo Favarolo
Original assignee: Zumtobel Lighting GmbH Austria
Current assignee: Zumtobel Lighting GmbH Austria
Priority date: 2019-11-25
Filing date: 2019-11-25
Publication date: 2021-05-26
Anticipated expiration: 2039-11-25
Also published as: EP3825604B1

Abstract

A light emitting assembly comprises a plurality of light sources (10) arranged on a support member (5) and an optical element (30) comprising a plurality of lenses (25) associated with the light sources (10), wherein the support member (5) together with the optical element (30) encloses at least one cavity, and wherein the assembly comprises filling means (40) which substantially fill the at least one cavity.

Description

The present invention relates to a light emitting assembly comprising a plurality of light sources arranged on a support member and an optical element with a plurality of lenses wherein the support member together with the optical element encloses at least one cavity. The light emitting assembly according to the present invention is in particular used in luminaires for outdoor and / or industrial applications.
With the introduction of LEDs as light sources for luminaires, the possibility to effectively divert the light has made the use of lenses a well established solution. As LEDs are very small light sources compared to classical light sources like incandescent bulbs or fluorescent lamps, optical elements are required which are specifically adapted to influence all light emitted by an LED in an efficient way. In view of these requirements, lenses have proved to be the most efficient optical solution for redirecting the light of an LED in order to obtain a desired light emitting characteristic. The different reflection indices of the lens material (usually suitable polymers or glass) and of the air allow the total reflection of the ray beams having a certain angle of incidents with respect to outer surfaces of the lenses. In this way, it is possible to effectively divert the light as needed by the use of so-called TIR lenses.
When multiple LEDs are used in a luminaire, it is common to group them together in a so-called LED cluster wherein the LEDs are preferably evenly distributed over the surface of a planar support member.
For outdoor and / or industrial LED luminaires the LEDs and the circuitry used to provide power to the LEDs need to be protected against humidity and moisture in order to avoid damage or failure of the luminaire. A common solution of this problem is to use the optical element comprising the lenses to create a sealed chamber between the optical element and the support member of the LEDs or the housing of the luminaire by using a gasket between these two parts.
In the solution explained before, a cavity is formed within the luminaire, which is usually filled by air. The air enclosed in this cavity is then heated up during the operation of the luminaire and cools down again when the luminaire is switched off. When the air is heated up, since the volume of the cavity is fixed, the pressure increases and produces a force on the internal side of the sealing gasket. If this force is higher than the one opposed by the gasket itself, this part can be deformed and hot air can go out to the ambient. On the other hand, when the luminaire is switched off, a similar but opposed phenomenon happens and the external air can transfer into the cavity. The luminaire "breathes". As this air from the ambient can have a high relative humidity that can condense within the cavity if the temperatures are suitable, there is the risk that water is collected within the cavity resulting in a damage of the electric components.
In a further development of the above-explained concept, a permeable membrane is used which allows the exchange of air but does not allow the passage of humidity. However, such components are usually expensive and there is no guarantee that they still work reliable after some years of operation.
Accordingly, there is a need for a solution wherein the above problems can be avoided.
According to the present invention, the free volume occupied by air within the cavity between the optical element and the support member for the LEDs is significantly reduced in order to minimize the amount of air that could be exchanged through the gasket. This is achieved by using filling means which substantially fill the cavity enclosed by the support member and the optical element. As the amount of air enclosed in the cavity is significantly reduced, a small increase of the volume (for instance caused by the deformation of the gasket) would generate a big pressure drop within the cavity and would no longer impact the functionality of the sealing means.
Accordingly, according to the present invention, a light emitting assembly is provided which comprises:

a plurality of light sources arranged on a support member,
an optical element comprising a plurality of lenses associated with the light sources,

In the present invention, the support member can be any element forming a support for the light sources and the circuitry used to provide power to the light sources wherein the support element further encloses together with the optical element the mentioned cavity. Preferably the support member is a planar, plate like member wherein in the case where the light sources are LEDs or LED clusters the support member is preferably formed by a printed circuit board (PCB) or an assembly comprising a PCB such as a metal core PCB (MC PCB) or a metal plate comprising a PCB. As an alternative, also using curved support members would be possible.
The optical element according to the present invention comprises the lenses used to influence the light emitted by the light sources. In order to enclose the cavity together with the support member, the optical element preferably comprises a plate like portion, in particular a transparent light transmitting plate, which connects the lenses on a side opposite to the light sources. In this way, the lenses can be assigned individually to the light sources wherein nevertheless the optical element forms a sidewall enclosing together with the support member the cavity including the light sources.
Preferably, so-called TIR lenses are used to influence the light emitted by the light sources as such lenses have shown to be very efficient for influencing all light emitted by an LED. Accordingly, the lenses preferably have reflective surfaces reflecting light of the light sources by total internal reflection. In this case, the inventive filling means of course should not or at least not significantly influence the efficiency of the lenses. Accordingly, according to a preferred embodiment of the present invention, the filling means are separated from the reflective surfaces of the lenses by a gap, preferably by a gap of 0.15-0.30 mm, more preferably in the rage of 0.18-0.25mm, most preferably in the range of 0.20-0.22 mm. It has been found by the inventors that a gap of this size which is still filled by air allows the surfaces 22 to reflect light by total internal reflection. On the other hand, the gap is small enough to prevent the accommodation of a significant amount of air within the cavity.
Preferably the filling means are formed by a single filling element which could for example be connected to the optical element forming a unit which is then connected to the support member. This solution allows to arrange the filling element in a defined position with respect to the lenses ensuring that the efficiency of the lenses is not negatively influenced. As an alternative, it would also be possible to connect the filling element in a first step to the support member, for example to the PCB, wherein the optical element is afterwards added to this arrangement.
As the filling element shall not have any influence on the light emission of the light emitting assembly, this filling element can be generated of any suitable material. In particular, the material of the filling element could be identical to the material of the optical element. Preferably, the filling element is generated of an electrically non-conductive, not hygroscopic and rigid material, preferably from plastic.
In the preferred solution discussed above, the function of the TIR lenses is ensured by providing a gap between the total internal reflection surfaces of the lenses and the filling element. Alternatively, it would also be possible to cover the surfaces of the lenses used to reflect light by a reflective film or layer and filling completely the cavity enclosed by the support member and the optical element by a cast material. In this way, the amount of air entrapped within the cavity is reduced to a minimum and the best available protection for the LEDs and the circuitry is achieved. On the other hand, this solution results in a more complex and more expensive manufacturing process.
A still further solution to reduce the free space within the cavity would be to use a plurality of for example sphere-like filling elements having a small size, in particular a size substantially smaller than the size of the lenses, which filling elements are distributed in the at least one cavity. Although these elements are in direct contact with surfaces of the lenses which are used for total internal reflection, only point-like contacts would occur which would not significantly influence the function of the lenses. Nevertheless, also in this case the amount of air entrapped within the cavity can be reduced allowing to avoid the problems mentioned above.
Accordingly, the present invention provides an easy to realise an efficient solution to avoid the problems occurring in the prior art.
In the following, the present invention is explained in more detail with reference to the enclosed drawing. Figure 1 shows a cross sectional view of a luminaire comprising an inventive light emitting assembly.
The luminaire 100 shown in figure 1 is a luminaire used for industrial or outdoor applications as here often the above-mentioned problems occur based on temperature changes over time and high humidity in the ambient of the luminaire 100. Nevertheless, the present invention is of course not restricted to such specific types of luminaires but could be used in all cases where a protection of the light sources and electronic components is desired. In the present case, only those parts of the luminaire 100 relevant for the present invention are shown and explained. Other components like mounting elements or drivers used to drive the light sources obviously are also required but are not shown and are also not further discussed in the following.
In the case shown in figure 1, a matrix-like arrangement of LEDs 10 is used as light sources of the luminaire 100. In the following, these individual light sources 10 will be discussed as being single LEDs. However, it should be understood that each individual LED 10 could also be replaced by a small number of LEDs, for example by an RGB LED cluster or a pair of white light LEDs emitting white light with different colour temperatures. In case these LEDs can be separately driven, the colour or colour temperature of the light emitted by the luminaire 100 can be adapted.
As already mentioned, the LEDs 10 are arranged in a matrix-like manner on a planar support member 5 which is in the present case formed by a printed circuit board (PCB). This printed circuit board 5 is located on the bottom wall 2 of a housing 1 of the luminaire 100. Of course, it would also be possible to use small individual LED modules comprising in each case a small PCBs for a single LED or LED group which are then directly mounted on the bottom wall 2 of the housing 1. In this solution, the housing 1 itself or another element supporting the PCBs will be considered to form the support member enclosing the cavity together with the optical element which is explained in more detail afterwards. The support member also could be formed by a MC-PCB or an assembly formed by a metal plate comprising on ore more PCBs. However, preferably a single large PCB 5 is used supporting all LEDs 10 as it is shown in figure 1. The support is in most cases planar. Nevertheless, also curved support members would be possible.
LEDs emit light in several directions and therefore optical elements are required to influence the light such that a desired light distribution of the luminaire is obtained. In particular, so-called TIR-lenses has proved to be extremely efficient for redirecting the light of LEDs and thus the luminaire 100 shown in figure 1 comprises a plurality of such TIR-lenses wherein each lens 20 is assigned to one LED 10 or LED group. As it is known in the prior art, such a TIR-lens 20 comprises a truncated cone-shaped or truncated pyramid-shaped lens body 21 which diverges in a direction away from the LED 10. Usually, the lens body 21 comprises a small cavity facing to the LED 10 wherein the LED 10 extends at least in part into this cavity. The surfaces of this cavity then form the light entry portion of the lens 20.
The light emitted by an LED 10 under large angles (with respect to the main emission direction) and entering the lens body 21 is in particular influenced by the outer surfaces 22 of the lens body, which redirect the light preferably by total internal reflection. In this way, the light emitted by each LED 10 can be collimated by a TIR lens in an efficient way and then directly emitted by the luminaire 100 or further influenced by other optical elements. Alternatively, the surfaces 22 could be provided to tefelct the light in accordance with specific desired characteristics. For example, surfaces 22 could be diffuse/scattering, diffuse-reflective or transparent. Also using pattered reflective surfaces 22 would be possible.
Generally, it would be possible to use individual lenses which are separately attached to the PCB 5. However, in most cases it is preferred to combine these lenses 20 to an optical element 30 as it is shown in figure 1. This is achieved by providing a transparent light transmission plate 31 wherein the lenses 20 are formed on the surface of the plate 31 facing towards the LEDs 10. In this way, a single unit is formed which can be attached to the PCB board 5 improving the positioning of the lenses 20 with respect to the associated LEDs 10 and improving thus the manufacturing process of the luminaire 100. Preferably, that light transmitting plate 31 and the lenses 20 are manufactured by molding to form an integrated single entity.
Depending on the desired light emission characteristics of the luminaire 100, the light transmission plate 31 may have specific light influencing properties. For example, the light transmission plate 31 can be diffuse/scattering, diffuse-reflective or transparent.
Another advantage of the optical element 30 combining the lenses 20 is that not only the LEDs 10 are protected by the lenses 20 but the whole PCB surface by the optical element 30. In this way, further electric components being provided on the surface of the PCB 5 are protected and there is not the risk that a user touches these elements or the LEDs 10.
In addition to prevent touching of the LEDs 10 and other electric components on the PCB 5, the optical element 30 is also used to protect the LEDs 10 and electric components from moisture. This is achieved by using the optical element 30 to form a closed and preferably sealed cavity accommodating the LEDs 10 and other elements provided on the PCB 5. To form this cavity, the optical element 30 is connected to a member supporting the LEDs 10. This could for example be the PCB board 5 itself. In such a case the optical element 30 would be formed in such a way that a - not shown - surrounding wall faces towards the surface of the PCB 5 wherein both units are connected to each other for example by using a sealing gasket. Alternatively, as shown in figure 1 the optical element 30 could be connected to a sidewall 3 of the housing 1 by a sealing gasket 4. In both cases, a cavity is formed which accommodates the relevant electric components of the light sources 10 and is completely surrounded by the optical element 30 and a support member for the light sources 10.
As can be learned from figure 1, the cavity enclosed by the optical element 30 and the housing 1 comprises several areas which are usually filled by air. As this air could lead to the problems mentioned above, the present invention reduces these free spaces by inserting filling means in the cavity. As it can be seen in figure 1, these filling means 40 in particular occupy the spaces between the individual lenses 20 such that only minor areas remain which still are filled by air. Although the pressure of this air increases and is reduced depending on the temperature of the air, the resulting force acting on the sealing gasket 4 is small such that the function of the sealing gasket 4 is not influenced. In this way, entrance of moisture in the cavity can be efficiently avoided.
According to a preferred embodiment of the invention which is shown in figure 1, the filling means 40 are formed by a single filling element 45, which in the present case comprises a grid like structure with portions extending in the area between two adjacent lenses 20. This filling element 45 can for example be arranged on the PCB 5 wherein afterwards the optical element 30 is attached to the resulting structure. More preferably however, the filling element 45 is in a first step connected to the optical element 30 wherein the resulting assembly is then attached to the PCB 5. In both cases, the filling element 45 can be in direct or indirect (e.g. via a sticky tape) connection with the support member.
As explained above, in particular the side surfaces 22 of the lenses 20 influence the light of the LEDs 10 by total internal reflection. This function of these surfaces 22 should not be influenced by the filling means 40 and it is thus preferred to provide and arrange the filling element 45 in such a way that a small gap 25 remains between the outer surfaces 22 of the lens body 21 and the outer surfaces of the filling element 45. This gap 25 can be very small (for example in the rage of 0.15-0.30 mm, more preferably in the rage of 0.18-0.25mm, most preferably in the range of 0.20-0.22 mm) but it ensures that the lenses 20 can influence the light in the desired way by total internal reflection. It is important to note that this gap 25 is only required for the outer side of surfaces 22 of the lenses 20 which are used for total internal reflection. Although in figure 1 also a gap is shown on the surface of the light transmitting plate 31 of the optical element 30 with respect to the filling element 45, this gap is here not really necessary and the filling element 45 could be attached to the optical element 30 at these portions. For example, an adhesive could be used at these portions to connect the optical element 30 and the filling element 45. Another option to combine both units 30 and 45 would be to provide pins and corresponding recesses in both elements ensuring a defined positioning of the filling element 45 with respect to the optical element 30.
According to the above explanations, the filling element 45 has no influence on the light emission and light distribution of the luminaire 100. In particular, the filling element 45 does not influence the function of the lenses 20. In view of this, any suitable material could be used for the filling element 45 and the material can be transparent or also opaque. In particular, it would be possible to form the filling element 45 from a material identical to the material of the optical element 30. Preferably, a material is used which is electrically non-conductive, not hygroscopic and sufficiently rigid. In particular, a plastic material could be used.
Other solutions to reduce the free space in the cavity enclosed by the optical element 30 and the support member 5 are possible as well. In all cases, it is desired to influence the function of the lenses 20 as less as possible.
A first alternative solution is to cover the outer surfaces of the lens bodies 21 with a reflective film or layer in order to ensure that light is reflected on these surfaces 22 in the desired way. In this case, no gap is required to allow a total internal reflection of the light rays and thus the remaining free space in the cavity could be almost completely filled by a cast material. Although this solution allows to almost completely exclude any air from the cavity, the manufacturing process is more complicated than the preferred solution explained in connection with figure 1.
Furthermore, another option would be to use a plurality of small for example sphere-like filling elements which are filled in and distributed over the whole cavity. These small filling elements - which can be made for example of glass or plastic (e.g. glass or plastic beads) - again occupy the space within the cavity reducing the amount of air. Although these elements would be in contact with the outer surfaces of the lens bodies 21, only point-like or at least very small contacts would occur which have only a very small influence on the function of the optical element 30, in particular on the total internal reflection function of surfaces 22.
In all examples explained above, the amount of air in the cavity of the luminaire is significantly reduced and the "breathing effect" will no longer result in the entrance of moisture into the cavity. Therefore, in an efficient way, significant problems can be avoided.

Claims

Light emitting assembly comprising:
• a plurality of light sources (10) arranged on a support member (5),

• an optical element (30) comprising a plurality of lenses (20) associated with the light sources (10),
wherein the support member (5) together with the optical element (30) encloses at least one cavity,
characterized in
that the assembly comprises filling means (40) which substantially fill the at least one cavity.
Light emitting assembly according to claim 1,
wherein the support member (5) is planar or curved.
Light emitting assembly according to claim 1 or 2,
wherein the light sources are LEDs (10) or LED clusters, the support member (5) being preferably formed by a PCB or an assembly comprising a PCB.
Light emitting assembly according to any one of the preceding claims,
wherein the optical element (30) comprises a light transmitting plate (31) connecting the lenses (20) on a side opposite to the light sources (10).
Light emitting assembly according to any one of the preceding claims,
wherein the lenses (20) have reflective surfaces (22) reflecting light of the light sources (10) preferably by total internal reflection.
Light emitting assembly according to claim 5,
wherein the filling means (40) are separated from the reflective surfaces (22) of the lenses (20) by a gap (25), preferably by a gap (25) in the range of 0.15-0.30 mm, more preferably in the rage of 0.18-0.25mm, most preferably in the range of 0.20-0.22 mm.
Light emitting assembly according to claim 6,
wherein the filling means (40) are formed by a single filling element (45).
Light emitting assembly according to claim 7,
wherein the filling element (45) is connected to the optical element (30) forming an assembly which is connected to the support member (5).
Light emitting assembly according to claim 7,
wherein the filling element (45) is in direct or indirect connection with the support member (5).
Light emitting assembly according to any one of claims 7 to 9,
wherein the filling element (45) is generated of a material identical to the material of the optical element (30).
Light emitting assembly according to any one of claims 7 to 10,
wherein filling element (45) is generated of an electrically non-conductive, not hygroscopic and rigid material, preferably of a plastic.
Light emitting assembly according to one of claims 1 to 5,
wherein the filling means (40) comprise a plurality sphere-like filling elements having a size substantially smaller than the size of the lenses (20) which filling elements are distributed in the at least one cavity.
Light emitting assembly according to one of claims 1 to 4,
wherein surface portions (22) of the lenses (20) covered by a reflective film or layer are provided to reflect light, the cavity enclosed by the support member (5) and the optical element (30) being filled by a cast material.
Luminaire (100) comprising a light emitting assembly according to any one of claims 1 to 13.
Luminaire according to claims 14,
Wherein the luminaire (100) is for outdoor or industrial applications.