LUMINAIRE WITH MIRROR REFLECTORS CAPABLE OF PROTECTING AGAINST TROUBLESOME LIGHT SPOTS

Abstract: A luminaire consisting of a housing containing at least one lamp fitted inside a concave reflector, which is incorporated in the housing and which longitudinally extends above a row of small, transverse mirrors, each of the latter being fitted on its upper side with a light-reflecting cover, and its outer edges anchored in specially-pro­ vided recesses in the main reflector, characterized in that the shape of the light-reflecting covers is so designed that an observer, who looks obliquely or askance in the direction of the luminaire, fails to notice, outside of the therein fitted lamp (2) and its mirror image reflected on said reflector (3), the discomforting light spots caused by reflection from the transverse mirrors bouncing off the reflector (3), when this is viewed at an angle which in relation to the ceiling is less than 30-45°.

Description: The present invention relates to a luminaire with at least one tubular lamp and a longitudinal reflector extending along and above said tubular lamp and having such a concave shape that all the light tranversely emitted from the lamp leaves the luminaire directly or after reflexion, under an angle with a base plane larger than or equal to a shielding angle α for said luminaire, which shielding angle α is comprised between about 30 and 45°, said luminaire further comprising a row of small transverse mirrors situated beneath said lamp and comprising a lower part of substantially V-shaped cross-section with concavely shaped sides and an upper part with mutually substantially parallel sides which upper part has according to its longitudinal direction a substantially V-shaped upper edge, the lines of which V-shape are joined by means of a curved piece. Such a luminaire is known from French patent Nr. 2,554,549. In this known device, the V-shaped upper edge of the transverse mirrors forms an angle with said base plane equal to said shielding angle. Moreover, the upper edge of the transverse mirrors is situated very closely to the lamp. No covers are provided on the upper side of the transverse mirrors. In this known luminaire, the transverse mirrors can cause a light-output reduction of upto 20 %. In the luminaire according to the present invention, the upper sides of the transverse mirrors are provided with a cover for reducing the light-output reduction due to the presence of the transverse mirrors. However, when using transverse mirrors provided with a cover, there has to be aimed at providing low-level luminance in the usual angle of observation, or in other words, to prevent bright light spots due to reflexions on said covers from being visible within said shielding angle. By "usual angle of observation" we mean here the angle in which one predominantly looks in the normal practice of using his sight. For example, in carrying out a desk task consisting of reading and writing on a horizontal surface, we can consider as usual an angle of observation ranging from + 10° to the perpendicular of the desk top to angles lying on a horizontal plane (visual communications). For such task lighting it is common or desirable to construct the optical system in such a way as to prevent radiating large quantities of light allowing bright light spots to be visible within a beam shielding angle of 30-45° to the horizontal angle of observation. Similar inconvenient light spots often occur when use is made of reflectors incorporating transverse mirrors, which are already on the market. These disturbances are the result of reflexions on the flat, reflective strip of material one finds on these transverse mirrors. The most common methods used today to prevent these spots are the following : the covers placed above the transverse mirrors are either made of a substance which reflects very little light, such as black synthetic material or are painted black, thus leading to a more than 20 % reduction in light-output ratio ; no covers are used at all, thus creating less bright spots, due to the fact that only the raised edges of the V-shaped mirrors reflect the light - this still causes a more than 10 % reduction in light-output ratio ; the transverse mirrors provided with a cover extend so high in the luminaire (nearly or completely upto the shielding α angle ) that the spots which are formed are in principle not visible when looking at the luminaire according to such an angle that the lamp itself becomes visible, in other words the spots are hidden behind the lamp. The latter solution for preventing light spots is taught by EP-A-0122972. However, the small distance between the cover and the lamp results in higher losses of light and may have negative effect on the lamp. Moreover, it will be clear that such a close position of the transverse mirrors with respect to the lamp allows only one possible lamp-position. The invention here described aims, through the use of an optical system based on the original transverse mirrors, at directing the light in such a way that : 1) the task to be lit is illuminated in the most efficient way possible, thus creating optimum illuminance levels of light intensity and optimum luminance and/or colour contrast. The task lighting can regard for example reading, writing, drawing or VDU work, or it can involve assembling/checking various elements in industrial spaces ; 2) large quantities of incident light rays emanating from the luminaire are prevented from being beamed directly into the eyes of the observer from angles which hardly differ from the usual angle of observation, thus reducing the viewer's capacity to perceive small contrasts and/or details and, in so doing, creating a disability glare ; 3) surfaces, (even relatively small ones) which are highly luminant in relation to their normal backgrounds are prevented from being visible from angles which hardly differ from the usual angle of observation (psychological or discomfort glare). Besides the disturbance provoked by looking directly at the spots in the luminaire, reflexions from these highly-luminous spots onto a VDU can hinder the VDU operator's task. In order to direct the light in the way just described and to reduce the light-output losses, the luminaire according to the invention is characterized in that said upper part comprises a light-reflecting cover forming said V-shaped upper edge, the lines of which V-shape form an angle β' with said base plane which angle β' is smaller than said shielding angle α and which angle β' is at least so large that light reflected by said cover does not leave the luminaire under an angle smaller than said shielding angle α. In a preferred embodiment of the luminaire according to the invention, the lines of said V-shape, defined by the upper edge of the transverse mirrors, form an angle of about 28° with said base plate. This angle of 28° corresponds to an angle of 124° between the lines of the V-shaped upper edge. Since the shielding angle is usually comprised between 30 and 45°, it will be clear that different lamp-positions are possible, each corresponding to a different shielding angle comprised between the hereabove mentioned values. Other details and advantages of the invention will become clear from the following description of a luminaire, built in accordance with said invention. This description is to be seen solely as an example, and does not limit the invention. Figure 1 is a cross-section of the luminaire, according to the invention. Figure 2 is a longitudinal cross-section of a part of the same luminaire. Figure 3 is, on a different scale, a side view of a transverse mirror according to the invention. Figure 4 is, on a different scale, a side-view of the commonly used type of transverse mirror. The luminaire, in accordance with the invention specifications and as shown in the above-mentioned figures, consists essentially of a housing indicated as 1 in Figure 1. The elements and parts necessary for fitting at least one lamp 2 do not pertain to the essence of the invention itself, and will therefore not be described herein any further. A reflector 3 is mounted partially along each side and partially above the lamp 2. Seen in section, it is mainly concave. This reflector can consist of either a single piece or, as seen in Figure 1, three different parts. Along the whole length of the reflector 3 small transverse mirrors are mounted. The outer edges of these mirrors are fastened to the reflector 3 in specially-provided recesses. When seen in cross-section, both the transverse mirrors according to the invention, as well as those which have been in regular use until now, display, at least in part, a v-shaped section. In order to allow the invention to better emerge, reference is first made to the design shown in Figure 4. The commonly-used transverse mirrors 5 are mostly v-shaped in section, and their straight upper parts are fitted with a cover 6 that is clipped either above or onto the v-shaped part of the transverse mirror. In order to avoid beaming the amount of light by means of these covers in the "wrong" direction, and thus causing the above-mentioned discomforting light effects, these covers have until now either been painted with a highly light-absorbent material, such as matt black enamel, or made out of matt black synthetic material. The result is a reduction in the total amount of light emanating from the luminaire. According to the invention, the total amount of light beamed is kept at maximum levels, and an observer, who looks obliquely or askance towards the luminaire from an angle of less than 30-45° to the ceiling, no longer sees the discomforting light spots described above; in other words, if the observer is unable to see the lamp itself, he is equally unable to see any light spots. The transverse mirrors 4 (Figures 1, 2 and 3) consist of two rectangular parts 7, shown in longitudinal section, which both, when seen in cross-section, combine to form a v-shape. If the case may be, they can be made out of a single piece. The rectangular concave parts 7 of the transverse mirrors 4 are joined at the top to strips 8 consisting of two nearly-flat, parallel parts. Seen in front view or in longutudinal section, these strips have a v-shaped appearance. The lines of this v-shape cross one another, forming an angle β of at least 120°. An essential element for the invention is the fact that the angle α (formed between the tangent a of the lamp 2, and the tangent b with the reflector underside) does not have to concide with the angle β′ (formed by the tangent c with the upperside of a transverse mirror 4, and the tangent b with the reflector underside). The strips 8 run between the two lines of the v-shape along a curve which forms a tangential circular connection with the above-mentioned v-shaped strips. The strips 8 rise upwards at their outermost parts, and above them is a cover 9 made out of light-reflecting material. The shape of the cover 9 (the angles β′ and the rounded part beneath the lamp(s)) has been chosen in such a way that, combined with the uppermost longitudinal mirror and the lateral longitudinal mirrors 3, if one glances sideways from any angle which in relation to the horizontal plane is less than the angle α, hardly any highly-luminant spots or none at all would be noticeable. The light striking the cover 9 is then reflected at an angle greater than the angle α. The amount of light recuperated from the cover 9 in certain cases results in a more than 20% increase in the total light-output as comapred to certain other designs which make no use of this specially-designed, light-reflecting cover 9. The special curve of this cover 9, combined with the curving of the longitudinal mirrors 3, means that it is not necessary that the sides 8 of the transverse mirrors and the attached light-reflecting cover 9 are placed so high that angle β′ coincides, as it were, with angle α. The most common designs are those where angle β′ is approximately 28° and where angle α is approximately 40°, thus giving rise to the fact that the vertical strips 8 here fail to act as a "cover" for the light spots, which would then be visible on the longitudinal reflector 3 from an angle less than angle α. The flat strips 8 and the concavely-bent parts 7 can either be constructed out of a single piece or consist of two separate parts. As can be seen from Figure 1, it can be deduced that the shape of the light-reflecting covers 9, as in the design described above, has been worked out in such a way as to bring about the complete or practically-complete disappearance of the discomforting light spots which occur in most other designs and are visible from angles which are less than the strived after shielding angle α in relation to the usual angle of observation. An added important advantage is that this comes about without having to make use of strongly light-absorbent materials to cover the upperside of the transverse mirrors. This means that the quantity of light falling on the covers 9 of the v-shaped transverse mirrors 4 is either not absorbed by them or is not beamed in "discomforting directions", but instead is beamed by the proposed mirrored, light-recuperation system in such a direction that this quantity of light can be profitably made use of for increasing illuminance levels and luminance and colour contrasts during everyday sight tasks. The invention naturally is not limited to the above-mentioned designs, and several changes could be made to them without going outside the scope of the claims.

Claims: A luminaire with at least one tubular lamp (2) and a longitudinal reflector (3) extending along and above said tubular lamp (2) and having such a concave shape that all the light transversely emitted from the lamp (2) leaves the luminaire directly or after reflexion, under an angle with a base plane (b) larger than or equal to a shielding angle (α) for said luminaire, which shielding angle (α) is comprised between about 30 and 45°, said luminaire further comprising a row of small transverse mirrors (4) situated beneath said lamp (2) and comprising a lower part (7) of substantially V-shaped cross-section with concavely shaped sides and an upper part (8) with mutually substantially parallel sides which upper part has according to its longitudinal direction a substantially V-shaped upper edge the lines of which V-shape are joined by means of a curved piece, characterized in that said upper part (8) comprises a light-reflecting cover (9) forming said V-shaped upper edge, the lines of which V-shape form an angle (β') with said base plane which angle (β') is smaller than said shielding angle (α) and which angle (β') is at least so large that light reflected by said cover (9) does not leave the luminaire under an angle smaller than said shielding angle (α). A luminaire according to claim 1, characterized in that the lines of said V-shape form an angle of about 28° with said base plane. A luminaire according to either one of the claims 1 or 2, characterized in that said lower part is substantially rectangular when seen in the longitudinal direction of the luminaire.

Inventors: ADAMS, FRANS, TAEYMANS, FRANSISCUS
Applicants: "ETAP"
Application year: 1987
Main classification: F21V11
IPC codes: F21V11