WO1988009461A1

WO1988009461A1 - Light fixtures

Info

Publication number: WO1988009461A1
Application number: PCT/DK1988/000079
Authority: WO
Inventors: Kai SØRENSEN
Original assignee: Lysteknisk Laboratorium
Priority date: 1987-05-18
Filing date: 1988-05-17
Publication date: 1988-12-01
Also published as: DK160057B; DE3890413T1; SE462932B; SE8903860L; SE8903860D0; DK251387D0; AU1932688A; GB8924428D0; DK160057C; GB2245696B; GB2245696A; DK251387A

Abstract

Light fixtures with a reflecting reflector and comprising an oblong light source and a light grating. According to the invention at least some of the parts of the grating are inclined relative to the longitudinal axis of the fixture in such a manner that the light hitting a part of the grating is reflected into a side reflector whereby the curvature of the latter is utilized. As a result the grating need not comprise curved surfaces. In addition the geometric loss is reduced at the same time as the manufacture is simplified and the final structure is reliable.

Description

Title: Light fixtures

Technical Field

The invention relates to light fixtures with a reflect¬ ing reflector, said fixture including an oblong light source and a reflecting light grating.

Disclosure of the Invention

The reflector controls the light emission of the fittings in one of the two main planes of the fixture, i.e. the main plane perpendicular to the longitudinal axis of the light source. For this purpose the cross section of the reflector is composed of unwinder curves, segments of a parabola and other curve shapes generally used for a reflecting reflector.

Unlike the reflector the grating controls the light emis- sion of the fixture in the second main plane intersecting the longitudinal axis of the light source.

A reflecting grating comprises a plurality of transverse parts arranged perpendicular to the longitudinal axis of the light source. In practice these parts are often ar- ranged in connection with the lower parts of the reflecting reflector, i.e. the side reflectors, and said parts form an optical unit. This unit is often removable so as to allow a possible replacement of the light source. The upper part of the reflecting reflector is a top reflector permanently mounted in the fixture housing. Sometimes the top reflector is white-painted or has been omitted so as to provide the fixture with a certain amount of upwardly directed light.

In order to achieve a light control it is necessary to provide the grating parts with curved surfaces, i.e. with a parabolic cross section. In this manner the grating parts disclose a predetermined width at the top which ensures a so-called "geometric loss".

The most frequently used type of reflecting gratings is the parabolic cross grating shaped in such a manner that the light is limited to be emitted between two planes forming a predetermined cut-off angle a with the sounding line. Then the geometric loss is determined by the top side of the parts at least being the fraction 1 - sin α of the area open for the passage of the light downwards through the aperture of the fixture. The fraction is exactly the one indicated when the parts comprise a sharp edge at the bottom. When the lower edge of the parts is of a predetermined thickness the fraction is larger. Parabolic cross gratings are usually shaped to a cut-off angle in the range 45° -60°. In this manner the geometric loss corresponds to a fraction approximately in the range 0.13 (for 60") to 0.29 (for 49°). According to the invention at least some of the grating parts are inclined. As a result the light hitting a grating part is reflected into a side reflector, whereby the curvature of the latter is utilized so as to make it unnecessary to provide the grating with curved surfaces. In this manner the geometric loss is reduced at the same time as the manufacture is simplified and the final structure is more reliable compared to the known structures.

The grating parts are advantageously situated along a zigzag line, and they are preferably formed by a thin plate which can be slightly twisted.

Brief Description of the Drawings

The Invention is described in greater details below with reference to the accompanying drawings , in which Fig. 1 is a bottom view of an oblong light fixture with inclined parts,

Fig. 2 is a sectional view of the light fixture,

Fig. 3 illustrates a second embodiment of the light fix- ture,

Fig. 4 illustrates the intermediate portion of a side reflector ,

Fig. 5 illustrates a fixture with the cross parts slightly twisted, and

Fig. 6 illustrates a third embodiment of the light fixture.

Best Mode for Carrying Out the Invention

The light fixture of Fig. 2 comprises a reflecting reflec¬ tor including a top reflector 1 and two side reflectors 2. The fixture comprises furthermore an oblong light source 3 in the form of a fluorescent tube. A light grating 4 is situated below the fluorescent tube 3, whereby at least some of the parts of the light grating are inclined rela¬ tive to the longitudinal axis of the fixture. In this manner the light hitting a grating part is reflected into a side reflector whereby the curvature of said side re¬ flector is utilized and makes it unnecessary to provide the grating parts 3 with curved surfaces. As a result the grating parts 4 can be a thin plate not causing the so- called "geometric losses".

According to a concrete embodiment the light part is a top reflector 1 and an optical unit, cf. Fig. 3. The top reflector 1 is preferably shaped as an unwinder, whereas the optical unit comprises side reflectors 2 of a parabolic cross section, the grating parts being situated in said optical unit.

The aperture of the top reflector is a horizontal, uniform¬ ly light-emitting area of the width π multiplied with d., d. being the diameter of the light source. The optical unit comprises planar, vertical cross parts 4 of thin plate being reflecting on both sides. These parts follow a zigzag line when seen from the bottom in Fig. 1. The parts 4 form a predetermined angle, preferably in the range 30° -45°, with the longitudinal axis of the light source 4.

One of the apertures is defined by two coinciding parts forming an angle of 90° and appears in Fig. 4 together with the intermediate portion of a side reflector. Fig. 4 furthermore illustrates the reflection of the reflector ascribed to the reflection in one of the part sides, the reflection ascribed to the reflection in the other part side, and finally the reflection ascribed to the reflection in both part sides.

It appears that the portion in question of the side re- flectors 2 and the reflections thereof form a figure being defined on all sides by curved, reflecting surfaces. Therefore the embodiment ensures a light control in both main planes in the same manner as in connection with a common optical unit including parabolic cross parts 4.

It appears from Fig. 4 too that the side reflector 2 must be adapted to exposure from an area adjacent the top rim of the opposite reflection. The latter corresponds to the fact that the side reflector must be adapted to an aperture of a width almost twice the width of the aperture of the top reflector 1.

These conditions can be illustrated for a standard fluor¬ escent tube of a diameter of 26 mm and for a cut-off angle of 60". A more detailed calculation illustrates that the height of the optical unit Is 110 mis, to which the height of the top reflecror 1 of 33 -~ must: be added, which results In a total height of the fixture of at least 143 mm.

According to a second embodiment of the optical unit the cross parts 4 are twisted so as to meet one another in coinciding curves on the side reflector 2, cf. Fig. 5.

The total effect of separate and double reflections can- not be produced in a simple manner. In practice tests have, however, shown that the side reflectors can now be adapted to a width of an aperture corresponding to only about 1.5 the width of the aperture of the top reflector. Under che above conditions the height of the optical unit is thereby calculated to be 76 mm, which allows a reduction of the total height to only 109 mm.

The above embodiment is advantageous by the total height being reducible. Furthermore a particularly simple manu¬ facture of the optical unit is obtained.

According to a third embodiment the optical unit has figuratively speaking been drawn up about the fluorescent tube 3 in such a manner that a further reduction of the total height is achievable, cf. Fig. 6. According to a concrete embodiment the total building height of the reflector and the optical unit amounts to only 78 mm under the above conditions.

An additional advantage of the inclined grating parts following a zigzag line is that they brace the light fix¬ ture .

The grating parts are preferably made of aluminium. While the invention has been described by means of specific examples and in specific embodiments we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. Light fixtures with a reflecting and at least partial¬ ly curved reflector, said fixture comprising an oblong light source (3) and a light grating, c h a r a c t e r- S i s e d in that at least some of the parts (4) of the light grating are inclined relative to the longitudinal axis of the fixture in such a manner that the light hitting a grating part (4) is reflected into a curved side reflec¬ tor (2), whereby the curvature of said side reflector is 0 utilized.

2. Light fixtures as claimed in claim 1, c h a r a c¬ t e r i s e d in that the parts (4) of the grating are arranged along a zigzag line.

3. Light fixtures as claimed in claim 1, c h a r a c- t e r i s e d in that the parts of the grating form an angle of 30" -50° with the longitudinal axis of the fixture.

4. Light fixtures as claimed in claim 1, c h a r a c¬ t e r i s e d in that the parts (4) of the grating are formed by a thin plate which can be slightly twisted (Fig. 5) .

5. Light fixtures substantially as described above and with reference to the accompanying drawings .