FIELD OF THE INVENTION

The present invention relates to the warm dimming light emitting arrangement, and especially to the cooling of high lumen warm dimming arrangements.

BACKGROUND OF THE INVENTION

Incandescent and halogen lamps have an effect when dimmed called warm dimming or Black Body Line (BBL) dimming. This provides the visual effect of a warmer light when dimmed than when fully lit. This effect is used in ambiance light situations to provide a comfortable soft light, for instance in restaurants, lounges etc.

The BBL dimming effect is desired also when using LED luminaires.

However, the LED light sources will provide light of the same color temperature regardless of the light level. Therefore, to provide the BBL dimming effect, an amber colored LED light source is provided in the luminaire, which light source provides light of a warmer color temperature. When the normal LED light sources are set to maximum light output level, the amber LED light source is off. This may provide light of a color temperature of 2700K.

When dimming, light output level of the normal LED light sources will be decreased, and at the same time, the light output level of the amber LED light source will be increased. At a minimum light output level of the luminaire, the normal LED light sources will be off, and the amber LED light source will be at a maximum light output level. The light may then have a color temperature of approximately 2200K.

In order to achieve an acceptable optical performance, the light beam from the luminaire has to be axis-symmetric in all dimming modes. The amber LED light source, which normally is only one diode in each luminaire, with the warmer color will therefore need to be arranged in the centre of the light source arrangement, on an optical axis of the luminaire. The normal colored light sources will be symmetrically arranged around the amber LED light source.

For LED luminaires with high lumen output (approximately 400-600 lm), thermal management is an important issue to keep the light sources at optimal performance. The LED luminaire may therefore be provided with a fan for active cooling of the light sources. To ensure that all light sources in the luminaire are kept at a uniform performance level, a uniform cooling of all light sources is important. This is solved by a cooling air outlet at an optical axis of the luminaire, with the light sources symmetrically arranged around the outlet. Such non-dimmable LED luminaire may be found in CN102313180A.

When considering a LED luminaire with BBL dimming, the central position at the optical axis is occupied by the extra LED light source. A cooling air outlet is thereby not possible to arrange at the same location.

Consequently, there is a need for a high lumen LED luminaire with BBL dimming effect that ensures proper light quality and performance, proper beam shaping and at the same time ensures effective cooling over the whole dimming range.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide a light emitting arrangement with a BBL dimming effect and a desired beam shape, and with effective cooling over the whole dimming range.

According to a first aspect of the invention, this and other objects are achieved by a light emitting arrangement having an optical axis and which comprises a support member, a central solid state light source arranged on the support member at the optical axis, a set of solid state light sources symmetrically arranged around the central solid state light source on the support member, a heatsink in thermal contact with the solid state light sources, wherein the heatsink comprises at least two symmetrically arranged air inlets at a first radial distance from the optical axis, and at least two symmetrically arranged air outlets at a second radial distance from the optical axis, and a fan for providing air distribution from the outside of the light emitting arrangement through the air inlets and air distribution through the air outlets in the heatsink. The second radial distance from the optical axis is shorter than the first radial distance.

A dimmable high lumen arrangement may require both optical and thermal management, i.e. both beam shaping properties and cooling properties of the light sources need to be managed. An arrangement according to the present invention may provide optical performance required for a BBL dimmable luminaire, and at the same time provide cooling effective enough for a luminaire with high lumen output. By providing the set of light sources in a symmetrical arrangement around the central light source and the air outlets in the heatsink in a symmetrical arrangement, a uniform cooling for all light sources may be provided at the same time as a uniform beam shape may be provided as light output from the light emitting arrangement. This may further provide a uniform cooling over the whole dimming range such that all light sources may operate under the same conditions. Other configurations of the solid state light sources may be considered as well, e.g. when the central light source is positioned in the central area of the support member, but not necessarily on the optical axis.

The air inlets may be provided along a periphery of the heatsink. The symmetrical arrangement of the air inlets may provide a uniform air distribution to the fan from around the entire periphery of the heatsink. This facilitates the uniform air distribution to the light sources through the air outlets. The first radial distance from the optical axis to the air inlets may be larger than a radial extension of the support member. The support member may be arranged onto the heatsink and may thereby not cover the air inlets.

Alternatively, the support member may comprise openings or cutouts corresponding to the location of the air inlets in the heatsink.

In one embodiment, the light emitting arrangement may further comprise a light exit window arranged in front of the central solid state light source and the set of solid state light sources in a light exit direction, wherein the light exit window may comprise at least two symmetrically arranged window air outlets at a third radial distance from the optical axis. The light exit window may be provided with optics for optimal light output from the light emitting arrangement. To release the air from the light emitting arrangement, the light exit window may be provided with window air outlets. Air distributed from the fan, and that has passed the heatsink to cool the same, may thereby leave the light emitting arrangement through the light exit window. The window air outlets may in one embodiment be arranged at a radial distance from the optical axis that is substantially equal to the second radial distance.

The third radial distance from the optical axis may be different from the second radial distance. If the third radial distance is larger than the second radial distance, this may enable the light exit window to be provided with collimators arranged at locations corresponding to each light source on the support member. The air flow adapted to pass through the air outlet in the heatsink and the window air outlet may thereby be bent on its way out of the light emitting arrangement.

In one embodiment, the solid state light sources of the set of solid state light sources may be symmetrically arranged at a radial distance from the optical axis substantially equal to said second radial distance. The set of light sources and the air outlets in the heatsink may thereby together form a circle arrangement on the support member. The available space on the support member and in the light emitting arrangement may thereby be utilized efficiently.

In a further embodiment, the set of solid state light sources and the central solid state light source may be adapted to emit light of different wavelength. By providing the central light source as a light source adapted to emit light of a different wavelength than the light sources in the set of light sources, a BBL dimmable luminaire may be provided by using the central light source as light source for the low light output levels, which may provide light of a lower color temperature than the set of solid state light sources.

In another embodiment, the heatsink comprises at least one axially extending wall is arranged at each air outlet. The at least one axially extending wall may extend in an axial direction similar to a light output direction of the light emitting arrangement. The at least one wall may comprise a plurality of walls depending on the shape of the air outlet. The at least one wall may thereby comprise walls that together surround the entire or a part of the circumference of the air outlet. The at least one axially extending wall may increase the contact surface between the heatsink and the cooling air and thereby improve the heat removal. The at least one wall may further prevent external objects from reaching the electrically active parts on the support member, which otherwise may damage the light sources or compromise the electric safety. The at least one wall may further be used for direction of the air flow from the fan towards the outside of the light emitting arrangement through the air outlet. The at least one axially extending wall may form a continuous axially extending wall around the air outlet on the heatsink. By forming a continuous wall around the opening of the air outlet on the heatsink, air flow through the air outlet may at least partly be prevented from entering the space in the light emitting arrangement wherein the solid state light sources are located. This may prevent dust from being gathered in that space which otherwise would interfere with the optical performance of the light sources. Such wall may further improve the air flow direction and heat removal function of the heatsink.

In one embodiment, each air outlet on the heatsink may have a curve shaped. The curve shape of the air outlet may be a scoop shape. The curve shaped air outlets may provide a reduced pressure loss and increased cooling effect when the air passes the heatsink. It may further increase the contact surface area between the heatsink and the passing cooling air, thereby increasing the heat removal. Each curve shaped air outlet may comprise a lip member arranged to extend axially towards the fan. The lip member may be adapted to receive the air from the fan tangentially such that the air enters into the air outlet in a direction having an angle to the optical axis. The air flow from the fan through the air outlet is thereby disturbed in a lesser extent. The cooling effect of the heatsink by the distributed air may thereby be increased. The axially extending lip member may comprise a flat portion extending in a plane substantially perpendicular to the optical axis, and wherein said flat portion at least partly may cover the air outlet in an axial direction. Such flat portion may further facilitate the air distribution from the fan through the air outlets. Further, by covering at least a part of the air outlet in an axial direction, it may be avoided that long objects may be entered through the air outlets from outside the light emitting arrangement to reach the fan. This may increase the safety of the arrangement.

In one embodiment, each air outlet in the heatsink may be provided with axially extending bars. The air outlets may be provided with axially extending bars in order to increase the surface of the heatsink exposed to the distributed air from the fan. The bars may further be arranged for controlling the air distribution through the air outlets. Further, the bars may prevent external objects from reaching the electrically active parts on the support member.

In a further embodiment, the support member may comprise at least two air outlet openings in positions corresponding to the air outlets of the heatsink. The support member may be arranged in direct contact with the heatsink. The solid state light sources arranged on the support member may thereby be in close contact with the heatsink. Heat generated by the solid state light sources may thereby be distributed to the heatsink such that a cooling of the light sources may be performed. In order to enable the air distributed from the fan through the air outlets in the heatsink to proceed through the light emitting

arrangement, the support member may be provided with openings corresponding to the air outlets in the heatsink. If the heatsink comprises axially extending walls at the air outlets, these walls may be adapted to extend through the air outlet openings in the support member.

In one embodiment, the air inlets may be arranged for air distribution to the fan in a first substantially axial direction. The air inlets may be arranged to be facing in an axial direction in relation to the optical axis. The air adapted to pass through the air inlets towards the fan may be distributed in a first axial direction. The first axial direction may be a substantially axial direction, or at least having an axial component in a direction in parallel with the optical axis. Further, the air outlets in the heatsink may be arranged for air distribution from the fan in a second substantially axial direction opposite the first substantially axial direction. The air outlets may be arranged to be facing in an axial direction. The air adapted to pass through the air outlets from the fan may be distributed in a second axial direction. The second axial direction may be a substantially axial direction, or at least having an axial component in a direction in parallel with the optical axis. The second axial direction, or the axial component of the second axial direction, may be opposite of the first axial direction or an axial component of the first axial direction.

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

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

Fig. la is a top view of a light emitting arrangement according to an embodiment of the invention;

Fig. lb is a perspective view of a light emitting arrangement according to an embodiment of the invention;

Fig. 2 is a perspective view of a light emitting arrangement according to an embodiment of the invention;

Fig. 3a is a perspective view of a heatsink and a fan according to an embodiment of the invention;

Fig. 3b is a perspective view of a heatsink according to an embodiment of the invention;

Fig. 4a is a perspective view of a light emitting arrangement according to an embodiment of the invention;

Fig. 4b is a perspective view of a heatsink according to an embodiment of the invention;

Fig. 4c is a perspective view of a heatsink according to an embodiment of the invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.

Fig. la illustrates a light emitting arrangement 1 comprising a housing 10, a heatsink 20, a support member 30, a fan 40 and a light exit window 50. The light emitting arrangement 1 has a longitudinal optical axis X. The fan 40 is arranged in the housing 10 below the heatsink 20. The heatsink 20 comprises air inlets 22 arranged, as seen in fig. lb, at a first radial distance dl from the optical axis X and air outlets 24 arranged at a second radial distance d2 from the optical axis X. The second radial distance d2 is smaller than the first radial distance dl . The air inlets 22 provide fluid connection between the outside of light emitting arrangement 1 and an inner space of the housing 10 in which the fan 40 is arranged. An air tight seal is provided between the heatsink 20 and the housing 10. Preferably, the air inlets 22 are symmetrically arranged along an as large portion of the circumference of the heatsink 20 as possible. By providing an alternative attachment of the heatsink 20, the air inlets 22 may in one embodiment be provided as a single air inlet extending along the entire circumference of the heatsink 20.

The support member 30 is arranged to support light sources, preferably solid state light sources. The support member 30 may be a PCB (Printed circuit board). A central light source 34 is arranged in a central position, at the optical axis X on the support member 30. A set of light sources 32 is symmetrically arranged at a common distance from the optical axis X around the central light source 34. The central light source 34 is provided as an amber light source with a light output of warmer color temperature than the light sources in the set of light sources 34. The central light source 34 provides the amber light output in a BBL dimmable light emitting arrangement. The central light source 34 is adapted to be dimmable in an opposite order than the set of light sources 32. When the light output of the set of light sources 32 is decreased, the light output of the central light source 34 is adapted to be increased, and vice versa.

Other configurations of the solid state light sources may be considered as well. The central light source 34 can be positioned in the central area of the support member, but not necessarily on the optical axis, or there may be two or more central light sources 34 positioned in a symmetrical way around the optical axis.

The central light source 34 and the set of light source 32 generate heat. In order to secure optimal performance and desired light output from the arrangement 1, the light sources 32, 34 need to be cooled. The support member 30 is therefore arranged on the heatsink 20 and in thermal contact with the heatsink 20 to distribute the heat generated by the light sources 32, 34 to the heatsink 20. The heatsink 20 is made of metal to provide suitable thermal contact.

The air outlets 24 in the heatsink 20 enables air distribution from the fan 40 to cool the heatsink 20. The air outlets 24 are symmetrically arranged at the distance d2 from the optical axis X and the central light source 34.

In front of the support member 30 and the light sources 32, 34 in a light output direction along the optical axis X, a light exit window 50 is arranged. The light exit window 50 comprises collimators 54 arranged in corresponding positions as to the positions of the light sources 32, 34 on the support member 30. The light exit window 50 further comprises air outlets 52. The air outlets 52 on the light exit window 50 are symmetrically arranged around the optical axis X at a third radial distance d3 from the optical axis X. The third distance d3 is larger than the second distance d2 due to the presence of the

collimators 54. Each collimator 54 has a cone shape extending from each light source 32, 34 towards an outer surface of the light exit window 50 in the light output direction to direct the light from the light source 32, 34 in a desired way. The largest portion of the cone shaped collimators 54 are located at the outer surface of the light exit window 50, which thereby forces the air outlets 52 in the light exit window 50 to be arranged at a larger distance from the optical axis X than the air outlets 24 in the heatsink 20.

As further seen in fig. 2, the air inlets 22 in the heatsink 20 enables an air flow A from the outside of the light emitting arrangement 1 to the fan 40. An outer diameter of the support member 30 and the light exit window 50 being smaller than the radial distance dl of the air inlet location provides that the air inlets 22 are in fluid connection with the outside of the arrangement 1.

The air outlets 24, 36, 52 in the heatsink 20, support member 30 and light exit window 50 enables an air flow B from the fan 40 to the outside of the light emitting arrangement 1. The cooling air passing the heatsink 20 thereby removes heat generated by the light sources 32, 34.

When the fan 40 is operated, air will be distributed through the air outlets 24 in the heatsink 20. Air will then further be drawn by the fan 40 into the light emitting arrangement 1 through the air inlets 22. To provide a uniform air distribution over the whole range of the fan 40, the air inlets 22 are symmetrically arranged along the circumference of the heatsink 20. The arrangement of the air outlets 24 will provide a uniform cooling function over the whole extension of the heatsink 20 and the support member 30. This will enable all light sources 32, 34 to be cooled in a uniform manner via the heatsink 20, providing uniform operating properties for all light sources 32, 34.

As seen in figs. 1 and 2, the air outlets 24 in the heatsink 20 are provided with axially extending walls 21 around the opening in each air outlet 24. In different

embodiments, different number of sides around each opening may be provided with such walls 21. In the illustrated embodiment, all four sides around each opening are provided with walls 21. Alternatively, only one side, for instance the side of each opening facing towards the optical axis X, is provided with an axially extending wall 21, or three sides of each opening, including the side facing the optical axis X and the two radially extending sides of each opening may be provided with such walls 21. Such axially extending walls 21 at the air outlets 24 increase the contact surface between the cooling air and the heatsink 20, and thereby improve the heat removal. The walls 21 further prevent air from entering the space between the support member 30 and the light exit window 50, wherein the light sources 32, 34 are located. This will reduce the amount of dust being gathered at the light sources 32, 34, which otherwise would interfere with the performance of the light sources 32, 34. The axially extending walls 21 have a further function of preventing objects from outside the light emitting arrangement 1 reaching the electrically active parts on the support member 30. The radial extension of the light exit window 50 is smaller than the radial distance dl from the optical axis X to the air inlets 22. The light exit window 50 thereby does not interfere with the air flow A through the air inlets 22.

In an embodiment as illustrated in figs. 3a and 3b, the air outlets 24 in the heatsink 20 comprises openings which are located in a first plane Y of the heatsink 20, which first plane Y is substantially perpendicular to the optical axis X. Figs. 3a and 3b illustrate an embodiment of the invention wherein the heatsink 20 comprises four air outlets 24. The air outlets 24 in this embodiment are curved shaped, in a scoop manner. Each curve shaped air outlet 24 comprises a lip member 26 which provides a curve shape extending in an axial direction towards the fan 40 relative to the first plane Y. The lip members 26 are shaped to collect the air leaving the fan 40 tangentially, which reduces the pressure loss along the air distribution through the light emitting arrangement 1 and thereby improves the thermal performance. The lip member 26 further comprises a flat portion 28, which extends in a second plane substantially in parallel with the first plane Y of the openings in the air outlets 24 in the heatsink 20.

In one embodiment, each lip member 26 extends radially such that it covers an area at least as large as the respective opening when looked at in the axial direction. As further illustrated in fig. 4a, the air outlets 24 are provided with axially extending bars 23. The bars 23 provide a control function of the air distribution from the heatsink 20 towards the air outlets 52 in the light exit window 50. The bars 23 have a further purpose of increasing to protection effect of the axially extending walls 21 in preventing objects from reaching the electrically active parts of the light emitting arrangement 1.

In one embodiment, as illustrated in figs. 4b and 4c, each lip member 27 has a straight extension, axially towards the fan 40, with an angle to the first plane of the openings of the air outlets 24 in the heatsink 20. The lip member 27 thereby directs the air flow B from the fan 40 through the air outlet 24 with a reduced pressure drop across the heatsink 20. The lip member 27 may further comprise axially extending rips 29, extending in an axial direction towards the fan, for further direction of the air flow B. Turbulence or air flow disturbance may be reduced, as well as the contact surface between the heatsink 20 and the cooling air flow B may be increased.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the curve shaped air outlets may be formed in different ways to reduce pressure loss over the heatsink. Further, the heatsink may be modified in order to increase the contact surface between the heatsink and the passing cooling air.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person 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 or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.