Abstract
Today the use of false ceilings is decreasing as it involves too high an energy consumption. The tendency nowadays is to have bare concrete ceilings onto which luminaires are mounted, which often causes acoustical problems. The invention deals with these acoustical problems and relates to an illumination device (1) comprising a concave reflector (2) bordering, with an outer edge (3), on a light emission window (4). The reflector has a reflective surface (7) facing the light emission window. The illumination device further comprises lamp holding means (8) for accommodating a light source (9), and said lamp holding means being positioned in between the reflective surface and the light emission window. The illumination device is characterized in that the reflector is made of acoustically absorbing material.
Claims
1. An illumination device comprising: a pair of concave reflectors each made of a single acoustically absorbing and light reflective element and bordering, with an outer edge, on a light emission window, the pair of concave reflectors and the light emission window constituting a boundary of a reflector cavity, the pair of concave reflectors each having a reflective surface facing the light emission window, wherein the acoustically absorbing and reflective element is sufficiently rigid not to deform due to its own weight, wherein the single element of the pair of concave reflectors is configured to both absorb sound and reflect light in the illumination device, and wherein each of the pair of concave reflectors is attached to a top surface of a centrally positioned, elongated bridging element; a counter reflector made of a single acoustically absorbing and light reflective element and positioned such that a concave reflective surface of the counter reflector faces the reflective surface of each concave reflector, wherein the single element of the counter reflector is configured to both absorb sound and reflect light in the illumination device, wherein the counter reflector is attached to a bottom surface of the bridging element; and the bridging element configured to accommodate a light source on two opposing sides of the bridging element and being provided at or within the boundary of the reflector cavity in between the counter reflector and the reflective surface of each of the pair of concave reflectors.
2. The illumination device as claimed in claim 1, wherein each concave reflector is diffusely reflective.
3. The illumination device as claimed in claim 1, wherein the single acoustically absorbing and reflective element of either the pair of concave reflectors or the counter reflector is a sound absorbing foam.
4. The illumination device as claimed in claim 1, wherein the single acoustically absorbing and reflective element of the pair of concave reflectors or the counter reflector is flame resistant or heat resistant.
5. The illumination device as claimed in claim 1, wherein each concave reflector is tapered and comprises an edge wall connecting a narrow end of the pair of concave reflectors of width Woe and a wide end of the pair of concave reflectors of width Wlw, a height H of the pair of concave reflectors being a dimension measured substantially parallel to an axis A of the pair of concave reflectors and transversely to the light emission window, to the light emission window, the relationship between Wlw, Woe, and H being according to the following equation:
tan(a)<=(Wlw+Woe)/2H, with a is <=65.
6. The illumination device as claimed in claim 5, wherein the edge wall is curved for adapting a beam shape of light emitted by the illumination device.
7. The illumination device as claimed in claim 1, wherein the light source is at least one side-emitting LED mounted on a printed circuit board for issuing light from the light source in a direction transverse to the axis towards the reflective surface of each concave reflector.
8. A luminaire comprising at least a first illumination device as claimed in claim 7, wherein the luminaire comprises an acoustically absorbing panel with an optically reflective surface that comprises at least one surface with a plurality of concave surface elements, the first illumination device forming one of said concave surface elements.
9. The luminaire as claimed in claim 8, wherein the reflective surface of each concave reflector of the first illumination device provides a first beam, and wherein the luminaire comprises integral with the first illumination device at least one further illumination device with at least one further reflector for providing at least one further beam, the further illumination device forming a further one of said concave surface elements.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will now be further elucidated by means of the schematic drawings in which,
(2) FIG. 1 shows a cross section of a first embodiment of the illumination device according to the invention;
(3) FIG. 2 shows a perspective view of a luminaire in one piece, which is built up of a plurality of illumination devices similar to the illumination device of FIG. 1;
(4) FIG. 3A shows a cross section of a second embodiment of a luminaire comprising a plurality of illumination devices according to the invention;
(5) FIG. 3B shows a cross section of a third embodiment of a luminaire comprising a plurality of illumination devices according to the invention;
(6) FIG. 4A shows a second embodiment of the illumination device according to the invention;
(7) FIG. 4B shows a perspective view of a third embodiment of the illumination device according to the invention;
(8) FIG. 5 shows a ceiling with suspended luminaires according to the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(9) FIG. 1 shows a cross section of a first embodiment of the illumination device 1 according to the invention. The illumination device comprises a concave reflector 2 which borders, with an outer edge 3, on a light emission window 4, the reflector and light emission window constituting a boundary 5 of a reflector cavity 6. The reflector has a reflective surface 7 facing the light emission window. The illumination device further comprises lamp holding means 8 accommodating a light source 9; in FIG. 1 a plurality of white, red, green and blue (WRGB) light emitting LEDs are mounted on a PCB 10 with a light reflective surface 11. In this embodiment, the RGB LEDs do not render the right color for general illumination, but are added to the white LEDs to tune the color. Said PCB and LEDs together are provided in the reflector cavity, i.e. in this particular case form part of the boundary of the reflector cavity. The reflector is acoustically absorbing, diffusely reflective and flame resistant and heat resistant. The reflector is in one piece, tapered and comprises an edge wall 12 connecting a narrow end 13 and a wide end 14 of the reflector. The edge wall is made of sound absorbing foam and coated with GORE DRP, reflector material from Gore, a microporous structure made from durable, non-yellowing polymer PTFE (poly-tetra-fluoro-ethylene). The reflector is diffusely reflective, i.e. about 98.5% diffusely reflective and about 1.5% specularly reflective, rendering the light to be issued from the luminaire as a beam in a direction along an optical axis A. The illumination device is mounted in a housing 18 via which the illumination device is mounted to a deck/ceiling 19. A main part of the spacing 29 between the housing and the edge wall is filled with sound absorbing material. In this embodiment, said spacing and the edge wall are made of one and the same material (for the sake of clarity the edge wall is still indicated by a double line) and hence the edge wall is considered to have a variable thickness. The light source comprises a light-emitting surface 15 facing the light emission window, said light-emitting surface being arranged at the narrow end and being dimensioned substantially equal to the narrow end. The illumination device further has a mixing chamber 16 which is bound by the edge wall, the narrow end and an optical element 17 extending transversely to the axis and provided in between the light source and the light emission window. The optical element is a scattering element, in FIG. 1 a diffuser sheet with a sandblasted side 27 facing towards the light source and a side 28 facing away from the light source. The tapered reflector has at least a height H, H being a dimension measured substantially parallel to the optical axis A of the tapered reflector and transversely to the light emission window. The height H is the distance between the optical element 17 and the light emission window 4, which optical element is considered to be a substitute for the light source 9 as an (imaginary) shifted light source, along the axis A. The illumination device has a glare value, i.e. a value representing the level of glare, which satisfies the European Standard EN 12464 for rooms in which people work intensively with computer displays. The standard specifies requirements to control the average luminance values. For workstations, a maximum limit applies of 1000 cd/m.sup.2 for class I and II and 200 cd/m.sup.2 for class III of display screen classes according to the ISO 9247-1 classification. This limit applies for cut-off angles starting from 65 or more. The cut-off angle is the angle between the axis A perpendicar to the light emission window and the line at which light source and/or surfaces of high luminance are not visible anymore through the light emission window. The glare requirements for rooms in which people work intensively with computer displays pose demands on the illumination device with respect to its dimensions. In particular these demands result in a relationship between the width W.sub.lw of the reflector at its wide end 14 (corresponding to the width of the light emission window 4), the width W.sub.oe of the reflector at its narrow end 13 (corresponding to the width of the optical element 17) and the height H. This relationship is according to the following equation:
tan()<=(W.sub.lw+W.sub.oe)/2H,
with is <=65
(10) For critical computer screen activities the cut-off area is outside a cone around the axis A, the cone having a top angle of 110, said top angle being twice the cut-off angle of 55. The illumination device has a minimum shielding angle of 40, is the angle between the plane of the light emission window and the first line of sight at which any part of the lamp or its reflection becomes directly visible through the light emission window.
(11) FIG. 2 shows a perspective view of a luminaire 100 in one piece, which is built up of a plurality of illumination devices 1, 1 1 . . . similar to the illumination device of FIG. 1. The luminaire comprises a first illumination device 1 with a first reflector 2 for providing a first beam and, integral with the first illumination device, at least one further illumination device 1, 1 . . . , in this Fig. fifteen further illumination devices. Each further illumination device has one respective further reflector 2, 2 . . . for providing one respective further beam. The material of the reflectors of the illumination devices' luminaire is a lightweight open cell, thermo-formable foam. Adjacent the narrow end 13 of every illumination device but one (to make visible the narrow end 13), an optical element 17 is provided, in the Fig. a plate coated at a side facing the light source with a luminescent material 26, for example YAG:Ce which converts blue light from the light source to light of a longer wavelength. The coated plate partly transmits light from the light source and partly converts light from the light source, the balance between the transmitted light and the converted light being set such that said combination causes the light issued by the luminaire to be white.
(12) FIG. 3A shows a cross section of a second embodiment of a luminaire 100 with a plurality of illumination devices 1 according to the invention. Illumination device 1 is a luminaire with a round, cup shaped reflector 2 in one piece, which reflector borders, with an outer edge 3, on a round light emission window 4, the reflector and the light emission window constituting a boundary of a reflector cavity 6. The round reflector has a center 20 through which an axis A extends that coincides with an optical axis of the luminaire and extends transversely to the light emission window. In the center a light source 9 is provided on lamp holding means 8, i.e. a single side-emitting white LED mounted on a PCB, but this could alternatively be a halogen incandescent lamp provided with a mirroring coating on a side of its bulb surface facing towards the light emission window. Said LED issues light in a direction transverse to the axis towards the essentially diffusely reflective surface 7 of the round reflector; essentially in this respect means that the reflector is designed so as to be as highly diffusely reflective as possible, meaning that in practice it has a diffuse reflectivity of 93% or more. Light is issued from the luminaire as diffusely scattered light as shown by light rays 37. The reflector is made from sound absorbing material. In the luminaire, the two illumination devices shown are mutually separated by a reflector cavity 6 in which no light source is provided.
(13) FIG. 3B shows a cross section of a third embodiment of a luminaire 100 comprising a plurality of illumination devices 1 according to the invention, which is analogous to the luminaire of FIG. 3A, but in which the reflector cavity 6 without light source (see FIG. 3A) is substituted by a wave-shaped sound absorbing and light reflective mass 30 having a saw tooth structure when viewed in cross section. Said reflective mass preferably is of the same material as the material used for the edge wall 12 of the reflector 2.
(14) FIG. 4A shows a second embodiment of the illumination device according to the invention. The illumination device has a reflector 2 composed of two reflector parts 2a, 2b, i.e. two mirror-positioned elongated concave reflectors parts 2a, 2b, with undulated surfaces and which are mounted on a centrally positioned, elongated housing 18. The reflector has an outer edge 3 that borders on a light emission window 4. The reflector and the light emission window together constitute a boundary of a reflector cavity 6. Both reflector parts each have a respective inner edge 22a, 22b at which they are mutually separated by a spacing 23 through which the housing extends and at which they are mounted onto the housing. The housing houses driver electronics 32 for a light source 9. The housing extending through the spacing renders the driver easily accessible from the backside and enables easy connection of the driver electronics of the illumination device to a power supply. The illumination device further has two optical elements 17a, 17b, fixed in the housing and positioned transverse to the light emission window in the reflector cavity. The optical elements in combination with respective walls 34a, 34b of the housing, respective reflector parts 2a, 2b, and the light source 9, jointly forming respective mixing chambers 16a, 16b.
(15) FIG. 4B shows a third embodiment of the illumination device 1 according to the invention. The illumination device has a reflector 2 composed of two reflector parts 2a, 2b, i.e. two oppositely positioned elongated concave reflectors parts 2a, 2b which are mounted on a centrally positioned, elongated bridging element 21. The reflector has an outer edge 3 that borders on a light emission window 4. The reflector and the light emission window together constitute a boundary 5 of a reflector cavity 6. Both reflectors parts each have a respective inner edge 22a, 22b at which they are mutually separated by a spacing 23 and at which they are mounted onto the bridging element. The bridging element houses driver electronics (not shown) for a light source 9. The spacing between the reflector parts makes the bridging element easily accessible from the backside and enables easy connection of the driver electronics of the illumination device to a power supply, for example via electric cable 24. The illumination device further has a partly translucent, partly reflective counter reflector 25 mounted on the bridging element and positioned opposite the reflector in the reflector cavity. Both the reflector and the counter reflector are made of sound absorbing material. The light source, in the Fig. a plurality of LEDs but a pair of elongated low pressure mercury fluorescent discharge lamps would alternatively be possible, is mounted on the bridging element and is positioned in between the reflector and the counter reflector. Light issued by the light source either impinges on the reflector and is then largely issued from the illumination device to the exterior or impinges on the counter reflector and is then either diffusely transmitted through the counter reflector or reflected to the reflector and subsequently largely issued from the illumination device through the light emission window to the exterior.
(16) FIG. 5 shows a ceiling 19 where some of the conventional acoustic panels 38 that suspend from said ceiling are replaced by luminaires 100 according to the invention. Each of the luminaires comprises a plurality of illumination devices 1 distributed together with non-illuminating reflector cavities 6 over the luminaire.
