REFLECTOR FOR AN OBLONG LIGHT SOURCE

Abstract: A reflector for an oblong light source, comprising a conical Part (1) to which a curved part (2) connects. Said parts being provided on the inside with longitudinal grooves. A number of grooves in the curved reflector part (2) are provided with a reflection face (8) which runs parallel to the line through the starting point and finishing point of the groove bottom (6) of the curved reflector part (2) and is directed towards the centre line of the reflector.

Description: The invention relates to a reflector for an oblong light source, comprising a conical part to which a curved part connects, said parts being provided on the inside with longitudinal grooves. Light fittings with downward-directed light beams are used, for example, to direct light from the ceiling onto, say, the floor. Here, reflectors are used to direct the light as well as possible onto the object. For point-shaped light sources, virtually ideal reflec­ tor forms can be calculated, because point-shaped light sources do not stand in the way of the light beams reflected by the reflector. In particular, light dis­ tributions in which the light intensity increases as the angle relative to the centre line of the reflector in­ creases can be achieved. By means of such light inten­ sity distributions, which are also described as wing-­ shaped, a light intensity distribution which is as uniform as possible can be obtained on the area to be lit, for example the floor. Oblong lamps, such as compact fluorescent lamps are not point-shaped and therefore have a light-radiating and, conversely also, a light-absorbing surface which is so large compared with the dimensions of the reflector that the lamp constitutes a hindrance for the light rays coming from the reflector. This means that, without ad­ ditional measures, only light intensity distributions which are at a maximum at or near the reflector centre line can be obtained. In order to obtain a wing-shaped light distribu­ tion, applicants have developed a reflector cap, com­ prising a conical and a curved part. These parts are provided with longitudinal grooves. Viewed in the cross section of the reflector, the said longitudinal grooves are preferably triangular in shape. In this way, the light rays falling on the walls of the grooves are deflected in such a way that they run along the oblong light source and thus contribute to a wing shaping of the light intensity distribution. A precise calculation of the light intensity dis­ tribution which can be expected is almost impossible due to the multiple reflections, and it would be too inac­ curate, while the physical conditions have to be idealised. That is why, for the determination of the light intensity distribution produced by the lon­ gitudinal grooves or facets, one is dependent on measurements. Depending on the design of the reflector, it always happens that a further correction of the reflector is hardly possible, for example if material had to be added in the equipment for making the reflec­ tor in order to achieve the desired shape. Corrections of the curves of the curved part are very difficult to carry out and give rise to high costs. Despite the great difficulty and the costs, a uniform lighting intensity is not achieved. Moreover, the grooves give rise to a rotationally symmetrical wing-shaped light intensity distribution which means that in a plane perpendicular to the centre line of the lamp a light distribution is produced in which the light intensity is less in the centre than outside the centre. The object of the invention is to provide a reflector of the type referred to in the preamble, in which the above-mentioned disadvantages and problems are avoided, or the equipment can be adapted in a simple manner. This object is achieved according to the invention in that a number of grooves in the curved reflector part are provided with a reflection face which runs parallel to the line through the starting point and finishing point of the groove bottom of the curved reflector part and is directed towards the centre line of the reflector. Through sliding the said reflection face parallel more or less towards or away from the centre line of the reflector, a correction can be made in the centre of the area to be lit which is perpendicular to the centre line of the lamp. This correction is to some extent at the expense of the light intensity in the wings. A further correction is preferably compensated for by the fact that the grooves in the conical reflector part, which are in line with the grooves provided with the reflection faces in the curved reflector part, are provided with a second reflection face which is directed towards the centre line of the reflector and runs from the centre of the first reflection face and to a point of the bottom of the groove in the conical reflector part. The optimum compensation can be achieved by making the second reflection face run more or less in the direction of the starting point of the groove in the curved reflector part. The invention will be explained in greater detail below with reference to an embodiment illustrated in the drawings, in which: Fig. 1 shows a cross section along the line I-I of the reflector according to Fig. 2; Fig. 2 shows a bottom view of the reflector according to the invention; Fig. 3 shows a cross section along the line III-III of Fig. 2. The reflector cap according to Fig. 1 comprises a conical part 1 and a curved part 2. The reflector cap also has a part 3 which contributes to the light intensity in the wings, but in particular serves as a dazzle screen. The oblong lamp (not shown) must be on the centre line of the reflector cap, while the lower end of the lamp is at the level of the transition between the curved part 2 and the anti-dazzle part 3 of the reflector cap. On account of the fitting of the lamp, the other end of the lamp will be below the top end of the reflector cap. This fitting and the fastening thereof are not shown, again for the sake of clarity. The inside of the curved part 2 and the conical part 1 is provided with grooves 4. These grooves extend at least over the length of the lamp. The shape of the grooves is most clearly seen in Fig. 2. The grooves preferably run in zigzag fashion with peaks 5 and troughs 6. A number of grooves 7 are provided with a first reflection face 8 and a second reflection face 9. The profile of the faces can be seen most clearly in Fig. 3. The first reflection face 8 is directed towards the centre line of the reflector and runs parallel to the imaginary line through the starting and finishing point of the curved groove bottom. Through parallel sliding of this face, a correction of the light intensity in the centre of the area to be lit can be made. This correction is accompanied by a slight reduction in light intensity in the wings, in other words, those light rays which form a greater angle with the centre line of the reflector. A further correction can be achieved again by the second reflection face 9, which is also directed towards the centre line of the reflector, and which intersects the first reflection face 8 in the centre thereof and runs from the centre through to a point lying between the said intersection line with the first reflection face 8 and a point 10 of the bottom of the groove. The above effect can be further increased by setting the angle of this face relative to the centre line of the reflector. In some embodiments it has been found that the said point must coincide with the starting point 11 of the groove. One can determine experimentally how many and/or which grooves must be provided with the said reflection faces 8 and 9. In the embodiment shown with the predetermined dimensions and shape, it was found that an optimum was achieved if the reflection faces are used in every other groove. In order to permit determination of the optimum experimentally in a simple manner, the procedure is as follows. The angle of the groove is experimentally determined in such a way that a strong wing shaping of the light intensity distribution occurs. Thereafter, through filling up of the grooves and through selection of the place and degree of filling-up of the grooves, the optimum is sought with regard to as low losses as possible and the sort of influence on the light intensity distribution. When the optimum has been found, a correction to the equipment can be made, with the wall thickness of the reflector at the reflection faces 8 and 9 being equal to that of the remaining part of the reflector. The perpendicular of the reflection faces or tangential faces 8 and that of the second reflection faces 9 should preferably be in the same plane as the reflector normal. It was found that a uniform light intensity distribution on a face perpendicular to the centre line of the reflector can be achieved with imorovement of the original output.

Claims: 1. Reflector for an oblong light source, comprising a conical part to which a curved part connects, said parts being provided on the inside with longitudinal grooves, characterized in that a number of grooves in the curved reflector part are provided with a reflection face which runs parallel to the line through the starting point and finishing point of the groove bottom of the curved reflector part and is directed towards the centre line of the reflector. 2. Reflector according to Claim 1, characterized in that the grooves in the conical part, which are in line with the grooves provided with the reflection faces in the curved reflector part, are provided with a second reflection face which is directed towards the centre line of the reflector and runs from the centre of the first reflection face and to a point of the bottom of the groove in the conical reflector part.

Inventors: WILLING, ACHIM
Applicants: RAAK LICHT B.V.
Application year: 1987
Main classification: F21V7
IPC codes: F21V7