EP2312203A1

EP2312203A1 - Lighting device with mixing chamber

Info

Publication number: EP2312203A1
Application number: EP20090173121
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2009-10-15
Filing date: 2009-10-15
Publication date: 2011-04-20
Also published as: TW201124658A; WO2011045720A1

Abstract

A lighting device (10; 20; 30; 40) comprising a mixing chamber (1); and at least one solid state light source (6) arranged in said mixing chamber (1) is disclosed. The mixing chamber (1) is enclosed by at least two diffusive exit windows (2, 3), and at least one reflective wall (4); and the solid state light source (6) and the diffusive exit windows (2, 3) are arranged in relation to each other such that less than half of light that is reflected by one of the diffusive exit windows (2, 3) is directed toward the at least one reflective wall (4).

Description

TECHNICAL FIELD

The present invention relates to a lighting device comprising solid state light source and a mixing chamber.

BACKGROUND OF THE INVENTION

Lighting devices, such as household lamps or street light, for illuminating its surroundings conventionally comprises inter alia a light source and an exit window, such as a translucent globe of a traditional incandescent lamp.
Recently, solid state light sources, such as light emitting diodes, LEDs, are increasingly used in all types of lighting devices, due to for example their higher efficiency. An example of an illumination device comprising a LED is described in W02009/093163 . In W02009/093163 several LEDs are arranged in a mixing chamber having reflective inner walls and a translucent diffusive exit window. Light from the LEDs that reaches the exit window is partially transmitted and partially reflected back into the mixing chamber. Thereby a mixing of light is provided. The exit window may also be provided with a color converting luminescent layer (e.g. phosphor), sometimes referred to as "remote phosphor".
Although such devices generally provide efficient illumination, there are applications where it is desirable to obtain a higher efficacy and/or efficiency and a capability to illuminate a larger area.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solid state lighting device with high efficiency.
According to an aspect of the invention, the above is met by a lighting device comprising a mixing chamber and at least one solid state light source arranged in the mixing chamber. The mixing chamber is enclosed by at least two diffusive exit windows, and at least one reflective wall, and the solid state light source and the diffusive exit windows are arranged in relation to each other such that less than half of light that is reflected by one of the diffusive exit windows is directed toward the at least one reflective wall.
The present invention is based on the realization that the efficacy of the lighting device can be increased by having at least two exit windows, and by arranging them in relation to each other and to the at least one LED so that a larger part of the light that is reflected into the mixing chamber by one exit window is aimed at the other exit window. Thereby, fewer reflections will be required for the light to exit the mixing chamber, and the amount of light absorbed within the mixing chamber is thus minimized. Consequently, a great part of the light emitted by the at least one light source is also emitted by the lighting device to illuminate its surroundings.
Moreover, the different exit windows cause peak intensities of transmitted light in different directions, and may be directed to achieve a desired light distribution. That is, the light from the lighting device may illuminate a relatively large area, or several different areas.
The diffusive exit windows may comprise a translucent material, such as an organic material, for example polyethylene or polycarbonate, or an inorganic material, for example glass or ceramics.
Furthermore, the diffusive exit windows may comprise a luminescent material. Such a luminescent material may be phosphor, whereby, a part of the converted light will be converted to longer wavelengths. If the LEDs are blue, the exit window with phosphor will scatter the blue and converted light partially outward and partially inward back into the mixing chamber. By proper tuning, such as by tuning the thickness of a phosphor layer on the exit window, a white light source may be made. The efficiency of a remote phosphor system may be made much higher compared to white LEDs. Alternatively, instead of a separate layer of luminescent material on the exit windows, the luminescent material may be added to the exit windows, i.e. the luminescent material particles may be mixed with the material of the exit windows.
Further, two of the diffusive exit windows may extend from the reflective wall at an angle toward each other, so as to form a tapered end of the mixing chamber. The mixing chamber will thus have a generally triangular cross section. Such a form is favorable in that it may simplify the redirection of light to the second exit window after reflection in the first exit window. The two exit windows moreover may behave as a so called Lambertian radiator, wherein the highest intensity may be found perpendicular to the surface. This feature may be used to direct the peak intensities of light transmitted through the two exit windows to illuminate two different regions of a surface, so as to for example illuminate a street in a uniform manner. The angle between the exit windows in the tapered end may moreover be selected to determine the location of the maximum intensity.
In order to simplify direction of intensity as well as for obtaining a uniform illumination by the lighting device, the exit windows may have equal size and shape, so that the cross section is an isosceles triangle.
Furthermore, the exit windows may be connected to each other in the tapered end by an intermediate reflective wall portion. In this manner the direction of the intensity may be simplified, since no light escapes through the tapered end, but only through the exit window surfaces. The intermediate reflective wall portion may be a thin portion for merely attaching the exit windows at the tapered end, or a broader wall portion rendering the triangular cross section of the mixing chamber truncated. In either embodiment, the intermediate reflective wall portion may be selected in order to regulate the location of the maximum intensity as well as the total intensity and efficacy of the lighting device, depending on toward which direction the wall portion is reflecting light.
Further, the intermediate reflective wall portion may protrude into the mixing chamber, such that the intermediate reflective wall portion is not parallel to the opposite reflective wall. A protruding intermediate reflective wall portion may be advantageous, by increasing the intensity of the lighting device, since it may direct reflected light toward either one of the exit windows. The shape of the intermediate wall portion may be triangular, whereby one of its sides reflects light toward one of the two exit windows, and the other of its sides reflects light toward the other one of the two exit windows.
Moreover, the at least two exit windows may be curved, which may be advantageous and increase the efficiency even more. Curved exit windows may relatively easily be adapted to produce an improved light distribution, resulting in a more efficient lighting device. In addition, with curved exit windows the internal efficiency of the mixing chamber may be improved since a larger part of a projection of the solid state light source on the plane of the exit windows may lie outside the exit windows.
Further, the solid state light source may be mounted directly on the reflective wall, which may be advantageous due to that only a small part of the light hits the light source, where it is absorbed.
Moreover, each exit window may be located in a plane such that a larger part of a projection of the solid state light source on this plane lies outside the exit window. By arranging the exit windows in such a plane, absorption of light by the light source may be minimized, and the internal efficiency of the mixing chamber may be improved. For the same reason, the intermediate reflective wall portion may, in addition or alternatively, be located in a plane such that a larger part of a projection of the solid state light source on this plane lies outside the intermediate reflective wall portion.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The 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. 1 is a perspective view of a lighting device arranged as a street lamp;
Fig. 2 is a partly broken away perspective view of a lighting device according to the present invention.
Fig. 3 is a cross-section of a lighting device according to the present invention.
Fig. 4 is a cross-section of a lighting device according to the present invention, with a protruding reflecting wall portion.
Fig. 5 is a cross-section of a lighting device according to the present invention, with curved exit windows.
Fig. 6 is a cross-section of another example of a lighting device according to the present invention.
Fig. 7 is a perspective view of another example of a lighting device according to the present invention.

DETAILED DESCRIPTION

Referring to fig. 1-6, the present invention will be described in relation to a street lamp, although the lighting device may be advantageously applied also in for example ambiance lighting, back lighting, downlighters, etc. Hence, fig 1 illustrates a street lamp having a lighting device 10 which is secured to a pole 11 that is located by a street 12. The lighting device 10 comprises at least two translucent diffusive exit windows 2, 3 and at least one reflective wall 4 arranged to enclose a mixing chamber 1. In the illustrated case, the lighting device has a reflective base wall 4 and two exit windows to give the mixing chamber an essentially triangular cross-section. The lighting device further has a thin reflective wall portion 5 that connects the exit windows 2, 3 in the tapered end of the mixing chamber 1, and two reflective walls 7, 8 that in the illustrated example are triangular and closes both triangular ends of the lighting device 10. The lighting device 10 is arranged on the pole 11 so that the tapered end of the mixing chamber 1 faces the street 12. An array of solid state light sources, such as light emitting diodes, LEDs, (not shown in fig. 1) is arranged inside the mixing chamber 1.
The lighting device is described in more detail in relation to fig. 2, which is a partly broken away perspective view. Here, the LEDs 6 are arranged on a PCB plate 14 having a reflective surface to serve as a reflective wall 4. Here, the array of LEDs 6 extends on the PCB plate 14 along the length of the lighting device 10. The LEDs 6 could for example be arranged more centrally or elsewhere in the mixing chamber 1, by for example connectively suspending it at a distance from the PCB, yet producing an evenly distributed light toward the exit windows 2, 3. The exit windows 2, 3 may comprise a luminescent material. For example, the luminescent material may be phosphor that converts light from blue LEDs 6 into white light, when the light passes the exit windows 2, 3.
The LEDs 6 emit light toward the two exit windows 2, 3 where the light is scattered partially outward and partially inward back into the mixing chamber 1. More than half of the light that is reflected by one exit window 2, 3 is directly aimed toward the other exit window 2, 3, and vice versa, whereby a great part of the light emitted from the LEDs is also emitted by the lighting device 10, immediately or after only a few reflections within the mixing chamber 1. The locations of the LEDs 6 affect the efficacy of the lighting device 10, for example in that light reflected by the exit windows 2, 3 that hits a LED 6 will be absorbed. Although parts of the light will be absorbed by the LEDs 6 or the reflective walls 4, 5, 7, 8, a main part of the light will be aimed toward one of the exit windows 2, 3.
Further, the peak intensities from each exit window 2, 3 is illustrated by arrows, to illustrate that there are two peaks in two different directions. Here, the highest intensities are found perpendicular to the exit windows 2, 3, since the exit windows 2, 3 are planar.
Returning to fig. 1, light emitted at an exit window 2, 3 has its highest intensity perpendicular to the respective exit window 2, 3, whereby the two peak intensities from the two exit windows 2, 3 may be directed to uniformly illuminate the street 12 on two sides of the pole 11. It has been found that an opening angle of the tapered end of the mixing chamber of between 0° to 60° provides a uniform, essentially rectangular light distribution. The opening angle may for example be about 20° (in the illustrated example it is 22 °) to achieve an optimal uniform light distribution below the lighting device 10, such that the, here schematically illustrated, two light distribution areas 42, 43 from the two exit windows 2, 3 overlap. In comparison to traditional street lamps, the lighting device 10 of the present invention may hence illuminate a wider area along a street 12, by having peak intensities in two directions, whereby fewer lamps are needed.
Fig. 3-8 illustrates other examples of lighting devices according to the present invention.
Fig. 3 is a cross-section of a lighting device 20. Here, the intermediate reflective wall portion 5 that connects the tapered end of the triangular cross-section is wider, and parallel to the reflective wall 4.
In the example in fig. 4, the intermediate reflective wall portion 5 of the lighting device 30 protrudes into the mixing chamber 1. In the illustrated example, the intermediate reflective wall portion 5 has a triangular cross-section, whereby light that is reflected by one side 5a of the triangle is aimed at one of the exit windows 2, and light that is reflected by the other side 5b of the triangle is aimed at the other exit window 3. Such an arrangement further increases the efficiency of the lighting device 30, since more light will be directed toward and hence redirected by the exit windows 2, 3. It has been found that an opening angle of the cross-section of the triangular reflective wall portion 5 between 0° and 45° increases the efficiency.
In fig. 5, the exit windows 2, 3 of the lighting device 40 are curved in a convex shape.
Fig. 6 illustrates a lighting device 50 comprising four exit windows 2, 3, 15, 16. Each of the four exit windows, as well as the intermediate reflective wall 5 are arranged in planes, so that a larger part of the projection of the LED 6 on each of these planes individually, lies outside the exit windows and the intermediate reflective wall 5, respectively. That is, a larger part of the light that is reflected by any of these surfaces will not be absorbed by the LED 6.
Fig. 7 is a perspective view illustrating a lighting device 60, comprising four exit windows 2, 3, 22, 23. Two oppositely arranged exit windows 2, 3 or 22, 23 extend from the reflective wall 4 at an angle toward each other, so as to form a tapered end of the mixing chamber. That is, the four tapered exit windows form a translucent pyramid, which in the illustrated example is truncated at the tapered end by an intermediate reflective wall portion 5.
Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. For example the reflective end walls or other reflective sides may be displaced by transparent exit windows, to emit light in more directions. The lighting device may be less elongated, to form a lighting device with a more compact design, etc. Further, the exit windows may be facetted.
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.

Claims

A lighting device (10; 20; 30; 40) comprising:
a mixing chamber (1); and

at least one solid state light source (6) arranged in said mixing chamber (1),

characterized in that said mixing chamber (1) is enclosed by at least two diffusive exit windows (2, 3), and at least one reflective wall (4); and
wherein said solid state light source (6) and said diffusive exit windows (2, 3) are arranged in relation to each other such that less than half of light that is reflected by one of said diffusive exit windows (2, 3) is directed toward said at least one reflective wall (4).
The lighting device according to claim 1, wherein said diffusive exit windows (2, 3) comprise a luminescent material.
The lighting device according to claim 2, wherein said luminescent material is arranged as a layer on said exit windows (2, 3).
The lighting device according to any of the preceding claims, wherein two of said diffusive exit windows (2, 3) extend from said reflective wall (4) at an angle toward each other, so as to form a tapered end of said mixing chamber (1).
The lighting device according to claim 4, wherein said exit windows (2, 3) have equal size and shape.
The lighting device according to claim 4 or 5, wherein said exit windows (2, 3) in said tapered end are connected by an intermediate reflective wall portion (5).
The lighting device according to claim 6, wherein said intermediate reflective wall portion (5) protrudes into said mixing chamber (1).
The lighting device according to any of the preceding claims, wherein said at least two exit windows (2, 3) are curved.
The lighting device according to any of the preceding claims, wherein the at least one solid state light source (6) is mounted directly on said reflective wall (4).
The lighting device according to any of the preceding claims, wherein each exit window (2, 3, 15, 16) is located in a plane such that a larger part of a projection of the solid state light source (6) on this plane lies outside the exit window (2, 3, 15, 16).
The lighting device according to any of the preceding claims, wherein the intermediate reflective wall portion (5) is located in a plane such that a larger part of a projection of the solid state light source (6) on this plane lies outside the intermediate reflective wall portion (5).