A LIGHT FITTING

The present invention relates to a light fitting.

One problem with light fittings or light fixtures intended for different purposes, such as the illumination of roads, signs, the facades of buildings etc., is that the light fitting or light fixture is dimensioned to illuminate the intended area, which means that in addition to illuminating the area intended there is generated a large amount of stray incident light on areas outside the intended area.

Another problem with conventional light fittings or light fixtures is that the design of the fitting results in uneven luminance over the surface to be illuminated. This means that the light source involved must be given a strength which is sufficient to achieve sufficient illumination of those regions of the surface on which least light falls.

The International application PCT/SE03/01052 describes a light fitting which satisfactorily solves these two problems. The application describes a light fitting or light fixture that includes a light source, a reflector and a glass cover wherein the light source is of a generally punctiform configuration and wherein the reflector is designed for the emission of parallel light from the reflector. The surface of the glass cover includes a large number of lenses, each of which has a square or rectangular shape as seen in the direction of the light transmitted from the reflector and is adapted to diffract the asymmetry of the light so that a square or rectangular area on a surface perpendicular to the optical axis of the lens will be illuminated.

One problem remains, however, namely that the amount of light incident on different parts of the illuminated surface varies, even when the illuminated surface is well defined. A problem is also encountered in respect of illuminating roads for instance, where the light fittings or fixtures must be placed at a high level so as to illuminate greater distances along the road or, alternatively, to place the light fittings at a lower level but closer together.

Despite these measures, the illumination over a given area is uneven.

The present invention provides a light fitting that provides much more uniform illumination of an area than conventional light fittings.

The present invention thus relates to an illuminative light fitting that includes a light source, a reflector and a glass cover, wherein the light source has a generally punctiform configuration, wherein the surface of the glass cover includes a large number of lenses that are intended to diffract the light emitted asymmetrically so as to enable a rectangular area or a square area to be illuminated at right angles to the optical axis of a respective lens, and wherein the invention is characterized in that the glass cover includes mutually parallel and upwardly projecting crests formed by two mutually opposing side surfaces that are angled to one another; wherein each crest has a wave shape in its longitudinal direction such that the height of respective crests will vary; wherein the bottom surface between two mutually adjacent crests has a corresponding wave shape so that the height of said bottom surface will vary; wherein the width of the crest is either constant or varies at its base, causing the side surfaces of respective crests to have a wave shape which corresponds to the variations in height of the crests; wherein each wave section of a crest forms a prism for diffraction of incident light from the reflector; wherein the top angle of respective crests causes light to spread or propagate in a first direction; and wherein the wave shape of the side surfaces of respective crests cause light to spread in a second direction at right angles to said first direction; and wherein light from each prism illuminates part of the illuminated surface.

The present invention will now be described in more detail partly with reference to an embodiment of the invention illustrated in the accompanying drawing in which

Fig. 1 is a cross-sectional view of a light fitting according to the invention;

Fig. 2 is a cross-sectional view of a lens belonging to the light fitting;

Fig. 3 is a plan view of said lens;

Fig. 4 illustrates a first embodiment of said lens;

Fig. 5 illustrates a second embodiment of the lens;

Fig. 6 illustrates inclined crests; and

Fig. 7 illustrates wave forms provided in the glass cover.

Figure 1 illustrates a light fitting 1 which includes a light source 2, a reflector 3 and a glass cover 4.

According to the present invention the light source 2 has a generally punctiform configuration. Preferred light sources are gas discharge lamps that have a high luminous efficiency and a concentrated discharge. MPXL (Micro Power Xenon Light) or CDM (Ceramic Discharge Metalhalid) are examples of such light sources. These light sources have a light spectrum that lies close to that of daylight or natural light.

According to one preferred embodiment of the invention, the reflector 3 is parabolic so that the light outputted by the reflector will be parallel.

The surface of the glass cover 4 includes a large number of lenses 5 which are intended to diffract the light asymmetrically such as to illuminate a rectangular square area that lies at right angles to the optical axis 6 of each lens 5.

The lenses 5 in the glass cover include mutually parallel upwardly projecting crests 7 formed by two opposing side surfaces 8, 9 that are angled to one another. Each crest 7 has a wave form in the longitudinal direction of the crest such as to vary the height of respective crests. The bottom surface 12 between two mutually adjacent crests has a corresponding wave shape so that the height of said bottom surface will also vary. This is illustrated in figure 6. The width of respective crests 7 at their base 10 is either constant or varies, meaning that the side surfaces 8, 9 of the crests 7 will have a wave form corresponding to the height variations of the crests. Each wave section of a crest 7 therewith forms a prism for diffracting incident light from the reflector 3, wherewith the top angle of the crests 7 result in the propagation of light in a first direction and the wave form of the side surfaces 8, 9 of the crests 7 cause light to propagate in a second direction at right angles to the first direction, wherewith light from each prism illuminates a part of the illuminated surface or area.

According to one preferred embodiment of the invention each side surface 8, 9 of each wave section of a crest is outwardly convex, such that said side surfaces 8, 9 will define a double- curved surface.

According to a first embodiment illustrated in figure 4, the side surfaces 8, 9 of the crests have a varying inclination with regard to the surface 11 from which they project upwardly in the longitudinal direction of the crests above the surface 11 from the centre of said surface and outwardly towards the periphery 12 of the surface.

Figure 4 shows in full lines a cross-section of a crest 7 which has a height H at its highest point. The figure shows in broken lines a cross-section of the same crest at a distance along the crest from the position at which the crest has its highest point, wherein the crest has a height h.

According to a second embodiment illustrated in figure 5 the width of the crests 7 vary at their respective bases 10 across the surface 11 from which the crests 7 project upwards from the centre of the surface and outwards towards the periphery 12 of said surface.

Figure 5 shows in full lines a cross-section of a crest 7 that has a highest point H. The figure also shows in broken lines a cross-section of the same crest at a distance along the crest from the position in which the crest is at its highest, wherein the crest has a height h.

It will be noted that according to a further embodiment of the invention, the height of respective crests varies along their lengths and that the base of respective crests also varies along the length of the crests.

According to a preferred embodiment of the crests 7 the crests are inclined at an angle to the surface 11 from which they project and therewith are also angled to the optical axis of the light fitting, as illustrated in figure 7.

According to a preferred embodiment of the invention this angle of inclination varies across the surface of the glass cover 4.

According to a preferred embodiment of the invention the lenses 5 are formed by depressions in the glass cover 4.

According to another embodiment of the invention, the reflector 3 is parabolic, as illustrated in figure 1, so that the light leaving the reflector will be parallel when it meets the glass cover.

When the parallel light meets the glass cover, the light will be given an angle of propagation in a direction of the inclination of the crests towards the incident light arriving from the reflector. The spreading angle of the light in a direction perpendicular to the direction just mentioned is given by the wave shape of the crest.

According to a first embodiment of the invention, the crests 7 are formed on the surface of the glass cover 4 that faces towards the light source 2. The crests 7 are preferably formed in the manner described above with respect to the second embodiment of the invention and illustrated in figure 5. The benefit obtained with this particular embodiment is that the crests are kept protected against contamination while the outer surface of the glass cover is smooth and therewith readily cleaned by weather and wind .

According to a second embodiment of the invention, the crests 7 are formed on the surface of the glass cover 4 that faces away from the light source 2. The crests 7 are therewith preferably formed in the manner described above with reference to the first embodiment of the invention and illustrated in figure 4.

The first embodiment is beneficial by virtue of the fact that the angle at which the light is spread will be greater than the angle according to the second embodiment. This is because the parallel light arriving from the reflector passes through the planar inner surface of the glass cover as parallel light and is thereafter reflected towards the crests.

On the other hand, in the case of the second embodiment the light is reflected towards the crests by a further glass volume before the light is emitted from the planar outer surface of the glass cover 4.

The angles V at which the light is spread in the case of the first embodiment may reach to about +/- 75° to the optical axis of the light fitting.

In the case of the second embodiment, the angles V at which the light is spread may reach to about +/- 81° to the optical axis of the light fitting.

The present invention provides illumination with extremely high efficiency, by virtue of the fact that the optical system consisting of the lenses 5 in the form of crests 7 guides the light to the surface which is actually intended to be illuminated and therewith avoid wastage in the form of uncontrolled stray light.

Such a light fitting or light fixture can be used for many illuminative purposes. For instance, the fitting can be used to illuminate the outer facades of buildings, to illuminate signs, to illuminate camera studios and for greenhouse lighting, etc.

With regard to street lighting, the invention is highly beneficial in avoiding "black holes" between the light fittings, by designing the fitting so that it will illuminate a rectangular surface area of a street or road. This enables the total lighting effect to be diminished without losing visibility

he present invention thus avoids the aforementioned drawbacks.

It will be understood that the illustrated light fitting may have a form other than circular.

The present invention shall not therefore be considered restricted to the embodiments described above, since variations can be made within the scope of the accompanying claims.