AN ARRANGEMENT FOR ASYMMETRIC LIGHTING

Abstract: An asymmetric lighting device comprises a reflector (1) with a light source (3) provided in its rear portion. The reflec­ tor (1) surrounds and is closely adjacent the rear portion of said light source (3); preferably at a distance of 2 mm and it comprises a portion (4) screening the area directly below said light screen. The reflector (1) may be composed of trian­ gular facets. At the reflector (1) end most remotely from said light source (3) this portion may be truncated and replaced by one or more louver lamellae preferably three, which are in­ clined in an angle with the perpendicular on the working plane which is, preferably 56.3°.

Description: The invention relates to an asymmetric lighting arrangement of the kind stated in the preamble of claim 1. It is, among other things, required from a working lamp that the illuminating intensity on the working area should be high and uniform. Outside the working area illumination intensity should gradually decrease in all directions, including areas toward, below, and behind said lamp. It is also desirable that the light opening is at a rather small distance above the table, i.e. approximately 40 cm above the level of the working area, in order to avoid glare and ensuring a good distance between the front edge of the reflector and the center of the working area, which distance should be 40 cm. Furthermore, the size of the reflector should be as small as possible to avoid a dominating appearance and a structure that might be restrictive to work. A source of light especially considered for use is a so called PL-type fluorescent lamp. It is known to use PL-lamps in an arrangement according to the preamble of claim 1, for illuminating working areas with a reflector providing an asymmetric distribution of light, cf. e.g. LUXO-PL-410 manufactured by Jac.Jacobsen A/S which, however, brings about shadow effects on the working surface or area as well as illuminating the area below and behind the lamp too much. One object of the present invention is to avoid the above mentioned disadvantages. In an arrangement according to the preamble of claim 1 this object is achieved by means of a reflector having the features stated in the characterizing clause of claim 1. The nominal luminous flux of said lamps is 2000 lm. This quantity of light is, indeed, too large if it is permitted to illuminate the area close to the lamp without restriction. As follows from claim 1, it is, thus, suitable to remove part of the light flow directed straight down under the lamp. According to the invention this is achieved by the fact that the rear portion of the reflector encloses and is provided close to, but spaced apart from, the rear portion of the light source, thereby reflecting part of the light flow back onto said light source portion, so that the luminance of the light source is increased which will result in an increased lighting intensity on the most remote portion of the working area. The portion of the reflector surrounding the light source may be quite low, 4-6 cm, with a length normal to the light source of 20-30 cm. In order to enlarge the illumination of the light opening in breadth, side reflectors may also be provided. Such side reflectors may be curved or inclined so as to increase the light opening area still more. The forward reflector portion does not have the form of a continuous hyperbola or cylindrical surface since it is, as previously known, almost impossible to manufacture reflectors with such accuracy economically. There have been previous efforts to manufacture this reflector from several parallel faces which together formed an approximate hyperbola. As mentioned above in connection with the known lamp this, however resulted in illumination with undesirable striations. In order to avoid such striations the forward portion of the reflector is composed of triangular facets. As a consequence of this composition there will be diagonal overlaps in the light pattern removing striations. By providing the portion of the reflector most remote from the light source with a lattice, in the form of one or more louvre lamellae, the size of the reflector is substantially shortened and, at the same time, a fairly uniform illumination of the working area is achieved as in case of a corresponding larger reflector without any lattice. The invention will now be disclosed in more detail with reference to the drawings, wherein Figure 1 shows a diagrammatical embodiment of the reflector with the source of light, and Figure 2 shows the illumination intensity at a distance from the lamp with various embodiments of the lamp. Figure 1 is a diagrammatical elevational view in perspective of a lamp with a reflector 1 having a forward portion 6 with a hyperbolic profile with focus 7 at the lower edge of the light source 3. The light source is a so called PL-type fluorescent lamp. As regards the design of the lamp shade per se we refer to the disclosure below. The curvature of the substantially hyperbolic forward portion 6 is unambiguously determined by the direction of the axis of the hyperbola as well as its focal length. These parameters are selected so as to let the light opening be fully illuminated in the direction of the middle of the working area as well as its most remote area, cf. Figure 2 showing the working area at a distance from the source of light. Furthermore, the parameters are selected to have illumination decrease toward the point below the front edge 4 of the reflector, and the reflector meets the uppermost arm of the light source somewhat retracted from its highest point. If a (non faceted) hyperbolic shape were selected for the reflector the smallest defect of the reflector or in the arrangement of the light source (focusing) would result in undesirable shadows and accumulations of light in the working area. Furthermore, knuckle lines in the reflector extending in parallel with the light source will cause striations, cf. the previously known model PL 410. Theoretical calculations and experiments, on the other hand, show that if the knuckle line is inclined relative to the longitudinal direction of the light source, cf. Figure 1, striations will be avoided. As shown in Figure 1, the reflector is made from triangular facets 10 for the reason mentioned above. Reflector portion 4, as mentioned above, extends below the source of light to reduce illumination from said source of light to points immediately in front of the lamp. If this extension of the reflector shade ends with a straight line parallel with light source 3 there would be an abrupt change on the working surface from darkness to light, and this is undesirable. For this reason the termination of reflector portion 4 in relation to light source 3 is not designed as a straight line, but in a V-shape the source of light being gradually covered outwards towards the edge. However, the light source is at all places covered beyond its central line. Such a gradual covering of the light source ensures illumination without shadows below the working lamp with a gradual increase of light intensity as shown in Figure 2. The forward reflector portion 6 is constructed and calculated on the basis of a parabolic basic form with a cut-off direction of 45°. The forward portion 6 of the reflector 1 and the rear portion 8 thereof are joined at line 5 in a valley shape as indicated in Figure 1. This will reduce the efficiency of the lamp somewhat but it also reduces the focal length of the hyperbolic curve with the result that the amount of light at disposal is displaced further away in the working area, cf. the illumination curve in Figure 2 showing the preferred embodiment with curve I, and with curve II showing the illumination of the working area without the special joining of the front and the rear reactor portions and without a louver arrangement. To make the lamp itself shorter the portion of the reflector furthest off the light source is cut off and non-reflecting louver lamellae 2, e.g. painted black,are provided at this portion of the lamp. There may be one or more lamellae 2, but three lamellae 2 proved to be suitable. Said lamellae may be arranged at various angles relative to the perpendicular 9 to the table surface. Angles between 30° and 70° may be used, but the most suitable angle is 56,3°. The foremost portion of the reflector being removed, the lamp may be displaced closer to the working area and the lamp can still be provided at eye level without any hazard of glare. By providing a side mirror in the reflector the intensity of illumination of the working area may be somewhat increased. Measurements have showed that parallel side mirrors cause an increase of the intensity of illumination by approximately 10% in the closest portion of the working area, whereas there is a quite small increase of the intensity of illumination in the most remote portion of the working area. Also, there is an insignificant increase immediately adjacent the lamp. If the rear reflector portion was made of a conductive material, this could interfere with the discharge in the PL-lamp. This is probably due to the fact that the discharges in said fluorescent lamp create a magnetic field inducing an eddy current in the material, which in turn creates a magnetic field having an effect on the discharge. To prevent this it would be necessary to place the reflector at a distance 2 mm from the surface of the PL-lamp. In order to prevent such interference furthermore it is to be recommended to make the rear reflector portion 8 from a non-conductive material. The fact that the reflector is placed at a distance from the PL-lamp, as mentioned above, will also bring about a certain circulation of air about the PL-lamp preventing said lamp from reaching a temperature beyond the best working temperature. Experiments also showed that the circulation achieved in this manner is sufficient for the fluorescent lamp to emit the greatest possible illumination. Experiments also showed that if the reflector contacts the PL-lamp this causes a cold spot on the fluorescent lamp that will change colour in the long term by condensed mercury. Long-term experiments, however, showed that the above distance is sufficient to prevent such change of colour.

Claims: An asymmetric lighting arrangement comprising a reflector (1) in the form of a cylindrical surface having a forward portion (6), which is substantially hyperbolic, and a rear portion (8) adjacent an elongate lift source (3) whose longitudinal axis is aligned substantially parallel to the generators of said surface characterized in that the forward portion (6) of the reflector (1) is composed of triangular facets (10) having knuckle lines being inclined in relation to the longitudinal direction of the light source (3), and that the rear portion (8) of the reflector (1) encloses and is provided close to, but spaced apart from, the rear portion of the light source (3) and comprises a lower front edge portion (4) screening the area directly below the light source in its operating orientation. An arrangement as defined in claim 1, characterized in that the forward reflector portion (6), at the end opposite to the light source (3), is provided with one or more louvre lamellae (2). An arrangement as defined in claim 2, characterized in that said louvre lamellae (2) are inclined at an angle (α) to the perpendicular (9) on a working surface provided below the reflector (1), said angle preferably being 56.3°. An arrangement as defined in any one of claims 1-3, characterized in that the rear portion (8) of the reflector (1) is placed at a distance from the light source (3) in the range of 1-3 mm, preferably 2 mm. An arrangement as defined in claim 1, characterized in that the reflector (1) is provided with side mirrors, one at each side of the reflector. An arrangement as defined in claim 5, characterized in that the side mirrors are mutually inclined with the smallest opening therebetween provided near the light source (3). An arrangement as defined in any one of claims 1-6, characterized in that the lower front edge portion (4) below the light source (3) extends at least through a perpendicular plane containing the central axis of the light source (3), the termination of the lower front edge portion (4) not being parallel to the said axis, but preferably in a V-shape, so as to provide progressive screening of the light source(3).

Inventors: KROGSRUD, JENS CHR., SORENSEN, KAI O.
Applicants: JAC. JACOBSEN INDUSTRIER A/S
Application year: 1986
Main classification: F21V7
IPC codes: F21V7