Light fitting

The present invention relates to a light fitting.

One problem with light fittings for various purposes such as the illumination of roads, signs, facades, etc., is that the light fitting is dimensioned such that it illuminates the intended region, which means that in addition to illuminating the intended region, a large quantity of stray light is also produced, which impinges outside of the intended region.

Another problem is that the design of conventional light fittings entails these fittings giving an uneven luminance over the intended illuminated surface. This means that the source of light must be made sufficiently bright in order to achieve sufficient illumination of the regions of the surface on which the lowest intensity of light impinges.

A fitting is described in the international application PCT/SE03/01052 that satisfactorily solves these two problems. The said application describes a light fitting comprising a light source, a reflector and a glass cover, where the light source is of an essentially punctiform configuration and where the reflector is arranged to create parallel light when it exits from the reflector. The surface of the glass cover comprises a number of lenses, each one of which has a square or rectangular shape as seen in the direction of the light passing from the reflector, and is arranged to refract the Light in an asymmetrical manner such that a rectangular or square area on a surface that is perpendicular to the optical axis of the lens is i lluminafed.

One problem remains, however, namely that the amount of light that impinges on different parts of the illuminated surface varies, even if the illuminated surface is well-defined. A further problem in respect of illuminating roads, for exam- pie, is that the light fittings must be placed at a high level so as to achieve the illumination of a greater distance along the road. The light fittings may, alternatively, be arranged at a lower level, placed closer to each other.

Despite these measures the illumination over an area will be uneven.

The present invention offers a light fitting that provides a considerably more uniform illumination of an area than light fittings of the prior art.

The Swedish patent 528 795 describes a light fitting for illumination comprising a source of light, a reflector and a glass cover, where the source of light has an essentially punctiform configuration, where the surface of the glass cover comprises a number of lenses, arranged to refract the light in an asymmetrical manner such that a rectangular or sguare area on a surface that is perpendicular to the optical axis of the lens is illuminated. The invention according to the patent is characterised in that the glass cover comprises mutually parallel and upwardly protruding crests formed by two opposing side surfaces that are angled to one another, in that each crest has a wave shape in the longitudinal direction of the crest such that the height of the crest varies, in that the bottom surface between two adjacent crests has a corresponding wave shape such that the height of th^ bottom surface varies, in ^- hat "he ^nin of rhe ^resi jt its base is constant or varies, causing * ^~ .'\o si.ie surfaces it ^h^ crests

to have a wave shape that corresponds to the variations in height of the crest, whereby each wave section of a crest constitutes a prism for the refraction of light incident from the reflector, whereby the peak angle of the crests causes light to propagate in a first direction, and where the wave shape of the side surfaces of the crests causes light to propagate in a second direction at right angles to the said first direction, and in that the light from each prism illuminates a part of the illuminated surface.

A light fitting according to the said patent is based on the principle that total internal reflection takes place. The light fitting has one disadvantage depending on the fact that it is not possible to make the radius at the peaks of the crests sufficiently small, and this results in the formation of darker patches on the illuminated surface on both sides of the fitting. These darker patches are formed approximately 25-40° out from the crests.

The present invention solves this problem, and in this way significantly more uniform illumination is formed.

The present invention thus relates to a light fitting for illumination comprising a source of light, a reflector and a glass cover, where the source of light has an essentially punctiform configuration, where the surface of the glass cover comprises a number of lenses arranged to refract the light in an asymmetrical manner such that a rectangular or square area on a surface that is perpendicular to the optical axis of the lens is illuminated, where the glass cover comprises mutually parallel and upwardly protruding crests formed by two opposing side surfaces that are ϊrigl^d to one another, where each crest has a wave shape Ln the lopqitudi-

nal direction of the crest such that the height of the crest varies, where the bottom surface between two adjacent crests has a corresponding wave shape so that the height of the bottom surface varies, where the width of the crest at its base is constant or varies, causing the side surfaces of the crests to have a wave shape that corresponds to the variations in height of the crest, whereby each wave section of a crest constitutes a prism for the refraction of light incident from the reflector, whereby the peak angle of the crests causes light to propagate in a first direction, and where the wave shape of the side surfaces of the crests causes light to propagate in a second direction at right angles to the said first direction, and where the light from each prism illuminates a part of the illuminated surface, and is character- ised in that a part of the first-mentioned lenses has been removed in the centre of the said glass cover and replaced by a second lens, in that the said second lens comprises a number of lenses, where each one of these lenses has a square or rectangular shape as seen in the direction of the light pass- ing from the reflector, and is arranged to refract the light in an asymmetrical manner such that on a surface that is perpendicular to the optical axis of the lens a rectangular or square area is illuminated.

The invention will be described in more detail below, partly in association with an embodiment of the invention shown in the attached drawing, where

- Figure 1 shows in cross-section a fitting according to the invention, - Figure 2 shows in a schematic cross-section along a chord located outside a second lens according to the invention a iens t ^~ hαt belongs to the fitting, and

- Figure 3 shows schematically in plan view a lens according to the invention.

A light fitting 1 is shown in Figure 1 comprising a source of light 2, a reflector 3 and a glass cover 4.

The source of light 2 is of essentially punctiform configuration. Preferred sources of light are gas discharge lamps with a high light yield and concentrated discharge. Examples of such sources of light are MPXL (Micro Power Xenon Light) or CDM (Ceramic Discharge Metal halide). These sources of light have a light spectrum that is close to that of natural daylight.

According to a preferred embodiment of the invention, the reflector 3 is parabolic such that the light that exits from the reflector is parallel.

The surface of the glass cover 4 comprises a number of lenses 5, arranged to refract the light in an asymmetrical manner such that a rectangular or square area on a surface that is perpendicular to the optical axis 6 of each lens 5 is illuminated.

The lenses 5 in the glass cover comprise parallel protruding crests 7 formed from two opposing side surfaces 8, 9 at an angle to each other. Each crest ^η has a wave shape m the longitudinal direction of the crest such that the height of the crest varies. Also the bottom between two adjacent crests has a corresponding wave shape such that the height of the bottom varies. The width of the crest 7 at its base is constant or varying, causing the side surfaces 8, ' ^■ ) ct the crests 7 to have a wave shape that oorresDcnds *" o ^f he varia-

tions in height of the crest. In this way, each wave section of a crest 7 constitutes a prism for the refraction of light that is incident from the reflector 3, whereby the peak angle of the crests 7 causes light to propagate in a first direc- tion, and where the wave shape of the side surfaces 8, 9 of the crests 7 causes light to propagate in a second direction at right angles to the said first direction, and where the light from each prism illuminates a part of the illuminated surface .

Illumination with a very high efficiency is achieved through the invention according to the patent, by guiding light in the optical system consisting of the lenses 5 in the form of crests 7 to the surface that is actually to be illuminated and in this way avoiding waste in the form of uncontrolled stray light.

Such a light fitting can be used for all types of purpose. Examples of use are fagade illumination, sign illumination, illumination in photographic studios, greenhouse illumination, etc.

With respect to street illumination, the great advantage is that it is possible to avoid "black holes" between the fit- tings by designing the fitting such that it illuminates a rectangular area of the street. The total illumination power can also in this way be reduced without impairing visibility.

The factors mentioned above are described in more detail in the said Swedish patent, number 528 795.

According to ^re present invention, a portion of the tirst- named lenses b πre removed from t ^~ he centre of ^he said qLass

cover 4 and replaced by a second lens 10. This lens 10 is shown as a dark circular region in Figure 3. The second lens 10 comprises a number of lenses, not shown, of the type described in the said PCT/SE03/01052 , where each one of these lenses has a square or rectangular shape as seen in the direction of the light passing from the reflector, and is arranged to refract the light in an asymmetrical manner such that on a surface that is perpendicular to the optical axis of the lens a rectangular or square area is illuminated.

Through the fact that this second lens 10 refracts the light in a manner that is different from that of the first lens 5 with crests, the said dark areas on both sides of the fitting will be eliminated, such that a more even illumination of the illuminated area is obtained. The problem described in the introduction is in this way solved.

According to a preferred embodiment, the said second lens 10 is round.

According to a further preferred embodiment, the said second lens 10 has dimensions in the plane of the lens that are 25 to 35% of the corresponding dimensions of the first-named lens 5.

According to a further preferred embodiment, the lenses in the said second Lens 10 are formed on the surtace of the glass cover 4 that faces towards the source of light 2.

According to an alternative preferred embodiment, the lenses in the said second lens 10 are formed on the surface of the glass cover 4 that faces away from the source of light 2.

It is highly preferred that the reflector 3 is parabolic such that the light that exits from the reflector is parallel.

A number of embodiments has been described above. The second lens, however, may be manufactured as square or rectangular, and the lenses that comprise the second lens may be given another form than rectangular or square.

The present invention, therefore, is not to be considered to be limited to the embodiments specified above, since it can be varied within the scope of the attached patent claims.