A REFLECTOR FOR A LIGHT SOURCE

Abstract: To achieve a desired light distribution by means of a specular reflector composed of a plurality of plane, reflecting panels (15) the reflection coefficient is graduated over each individual panel. For this purpose the panels (15) are made non-reflecting in selected areas, preferably in a raster pattern (17).

Description: A reflector for a light source The invention concerns a specular reflector for a light source, composed of a plurality of plane, reflecting panels, in particular such a reflector as is used for guiding the light from the light source. The invention has its field of use within the graphic in- dustries, road illumination and for achievement of biolo¬ gical effects (solaria, greenhouses) where homogeneous illumination of a face is desired in certain cases, and a . certain deviation from homogeneity is desired in other cases. In apparatus for copying graphic drawings homogeneous illumination of a face whose extent corresponds to the drawing to be copied, is a necessity. In such apparatus the light source and its bowl-shaped reflector are fre- quently arranged in the bottom of the apparatus and with the light aperture of the reflector facing upwardly. The face to be illuminated is oriented horizontally and is disposed above the light source and the reflector. In such apparatus it is particularly desirable to reduce the dis- tance from the light aperture of the reflector to the face to be illuminated. This makes great demands on the dif¬ fusion of the reflector. For this purpose use is made of a reflector which is placed about the light source and which reflects part of the light from the light source to the areas of the face where the direct light from the light source is weaker than directly above the light source, so that the face is illuminated more uniformly. Such reflectors are known and are frequently composed of a plurality of reflecting faces, typically four, which are arranged symmetrically about the light source. Ideally, each of these faces is curved, but this ideal, curved face is frequently approximated in practice by angularly dis¬ posed and contiguous, plane panels since this facilitates the production. In such known reflectors each individual plane panel contributes with reflected light to supplement the illumination in a specific area of the face to be il¬ luminated. Each individual reflecting, plane panel is dimensioned and angularly disposed so that it reflects light to a specific part of the face to be illuminated. It is known that the bending lines between such panels may be parallel or form acute angels with each other, so that the panels will have the shape of acute-angled triangles. The Danish Design Registration MA 1827 1990 discloses such a reflector where each individual reflecting panel is pro¬ vided with a coating near the internal edges of the re¬ flector, which equalizes differences in illumination to a limited degree, preferably along the diagonals of the illumination face. However, in all known reflectors of the mentioned type in- homogeneities in illumination will invariably occur owing to overlap of the light from various panels. Additionally, each individual plane, reflecting panel will not contri¬ bute homogeneously to illuminate the illumination face, since illumination of a point on the face diminishes with the distance of the point from the reflecting face, i.e. toward the edges and corners of the illumination face. The object of the invention is to provide a reflector of the present type where each individual curved reflector sub-face is composed of a relatively small number of plane panels which in combination are a good approximation to the curved sub-face, and where the illumination distribu- tion, in spite of the small number of plane panels is more homogeneous than before and can even be controlled to a certain desired deviation from homogeneity through the aid of the same means. This object is achieved by graduating the reflection co¬ efficient of the individual plane panels over the panel, as stated in claim 1. This primarily makes it possible to control the illumination contribution of each individual, plane reflecting panel. This also makes it possible to approximate the ideally curved sub-faces of the reflector with a relatively small number of plane panels, while their overlapping illumination of the illumination face can now be controlled by graduating the reflection coeffi- cient. Claims 2 and 3 define expedient forms of graduation of the reflection coefficient which can be performed in a simple manner, e.g. by applying a non-reflecting layer or by mat- ting (e.g. by sand blowing or etching) in raster pattern on a punched plate before the plate is bent. Such a raster pattern may consist of spots (dot raster) or of streaks (line raster), where the size of the spots and the width of the streak, respectively, and/or the distan¬ ces between these may vary. This art is known from the photographic industries where it is used for reproducing shades of grey in photographic images for printing. The invention will be explained more fully below on the basis of some preferred embodiments of the reflector of the invention with reference to the drawing, in which fig. 1 is a perspective view of a preferred embodiment of the reflector of the invention, and figs. 2 and 3 show parts of a reflector according to the invention. Fig. 1 shows a bowl-shaped reflector 10 with the opening facing upwardly, and in whose bottom a light source is to be positioned. The reflector 10 is composed of four uni¬ form sub-faces 11 and thus has a square cross-section in each horizontal plane. For another use, the reflector 10 might have a rectangular horizontal section or be composed of a larger or smaller number of sub-faces 11. Each of the sub-faces 11 is made from a plate by bending along a plu¬ rality of bending lines 12, which are parallel in this case, but might form acute angles with each other. Thus, each of the four bent sub-faces 11 of the reflector con-. sists of a plurality of plane panels 15, and the four sub- faces 11 are joined to a bowl-shaped reflector 10 along their edges 13. The electrical connections of the light source are passed through openings 18. The inner side of the reflector is substantially specu¬ larly reflecting, but the panels 15 are provided with a coating, there being applied a non-reflecting layer 14 in certain areas, here shown in black. Each of figs. 2 and 3 show a sub-face 11 with bending lines 12, but before the plate is bent. Further, the coated areas are visible. Fig. 2 shows schematically a sub-face 11, where each of the plane panels 15a-f show possible examples of how the reflection coefficient may be graduated in practice. Panels 15a and 15b have a coating in form of parallel streaks. Panel 15c has a coating in a pattern of lines or narrow curves. Panel 15d has a coating with curves having varying width and mutual distance. Panels 15e and 15f each have a coating constituted of narrow acute angled tri- angles. Furthermore all the panels 15a-f carry a coating in zones near their ends. Fig. 3 shows that each panel 15 is formed with a pattern of dots, where each panel 15 is made non-reflecting in a pattern of varying density of dots. Both the curve patterns in fig. 2 and the dot pattern in fig. 3 serve to graduate the reflection coefficient over the respective panel 15, such-that the contribution of the panel to the illumination can be controlled individually. The patterns in figs. 1 and 2 are curve raster patterns, and the pattern in fig. 3 is a dot raster pattern. The re- flection coefficient can be graduated in a simple manner with these patterns, there being various optimization methods for calculating their designs with a view to light control for the task in question. The curve patterns of panels 15a-c in fig. 2 are shown with curves or streaks of a constant width, and the graduation of the reflection coefficient has been achieved by varying the distance between the streaks which consti¬ tute the pattern. This variation may be replaced by or be supplemented with a variation of the width of the streaks like in panel 15d. Similar considerations apply to the dot pattern in fig. 3, where the size of the dots and their mutual distance and distribution over the panel can be varied. Alternatively, each individual curve 16 in fig. 2 may re¬ present locations of constant reflection coefficient so that between two arbitrary curves there is throughout a constant difference in reflection coefficient which can vary continuously or stepwise between two curves. On the basis of a desired light distribution, the reflec¬ tion coefficient of each individual sub-face 11 can be calculated preferably by means of computer based methods for each individual sub-face, and it can be decided how the reflection coefficient is to be distributed over the sub-face. It is then a relatively uncomplicated task for the skilled person to transform the distribution thus calculated to e.g. a raster pattern which realizes the desired reflection and light distribution.

Claims: P a t e n t C l a i m s 1. A specular reflector for a light source, composed of a plurality of plane, reflecting panels (15), c h a r a c ¬ t e r i z e d in that on each of the panels the reflec¬ tion coefficient is graduated over the panel. 2. A reflector according to claim 1, c h a r a c t e r - i z e d in that selected areas of the panels are non- specular by reflecting. 3. A reflector according to claim 2, c h a r a c t e r ¬ i z e d in that the selected areas form a raster pattern.

Inventors: DUEDDER ULRICH, DUEDDER, ULRICH
Applicants: JESSEN JUERGENSEN A S H, UNILIGHT APS, H. JESSEN JUERGENSEN A/S
Application year: 1991
Main classification: F21V7
IPC codes: F21V7