WO1982001930A1

WO1982001930A1 - A double grid for fluorescent lamp units

Info

Publication number: WO1982001930A1
Application number: PCT/DK1981/000111
Authority: WO
Inventors: Sven A Willumsen; Steen Willumsen
Original assignee: Sven A Willumsen; Steen Willumsen
Priority date: 1980-12-03
Filing date: 1981-12-02
Publication date: 1982-06-10
Also published as: EP0065968A1; NL8120461A; FI822660L; GB2103778A; SE8204544D0; FI69353B; SE451091B; FI69353C; SE8204544L; FI822660A0; GB2103778B

Abstract

The grid comprises a plurality of light passages (3) surrounded by walls (4, 5, 6, 7) of an appropriate height and located at a mutual, appropriate distance permitting light from a light source (9) to flow through said light passages. The grid comprises at least two independent plane parallel grid members (1, 2) located closely to each other or at a predetermined mutual distance. By means of retaining means (8), e.g. short, snap-lock-like connections, the grid members may be secured to each other. The grid members may be of the same or different type in such a manner that both for instance may be shielding grids, or one grid member may be a shielding grid whereas the other, preferably the lower grid member may be a mirrored low luminance grid. By manufacturing the grid of two mutually spaced grid members, it is possible to place the walls (4, 5, 6, 7) at a greater mutual distance than previously, which ensures a material saving while maintaining the shielding angle usually aimed at. Such a construction furthermore ensures that the thickness of the walls may be reduced compared to known grids, which involves an additional material saving. The total weight of the grid is thereby essentially reduced. Furthermore, new light effects are permitted by providing the grid members with different colours.

Description

Title: A Double Grid for Fluorescent Lampt Units.

Technical Field

The present invention relates to a grid for fluorescent lamp units preferably for ceiling or wall illumination and comprising a plurality of cells defined by walls of an appropriate height and located at regular intervals permitting light to flow through said cells.

Background Art

Such a grid is known from Danish Patent Application No. 3542/76 dealing with a low luminance grid, which comprises two grid plates which are situated on top of each other and of different height. Both these grid plates are shaped as low luminance grids, i.e. mirrorred grids, where all the walls or slats comprise curved surfaces. The curvature of these curved surfaces faces away from the light source in such a manner that the larges opening faces towards the illuminated object, towards which the light controlled by the curved, mirrorred walls is transmitted as a pencil of rays. The grid plates are positioned directly on top of each other by part of one plate engaging grooves in the other plate. This known grid requires a relatively large amount of material for the manufacture and furthermore a mould for the manufacture of each grid, which increases the production cost. The grid manufactured in this manner is relatively heavy.

French patent specification No. 933350 discloses a grid comprising substantially triangular walls, one triangular apex of which faces away from the ligth source, said walls being woven together as in a sieve. However, this grid seems to be rather difficult to manufacture.

Furthermore several different either low luminance or shielding grids are known, which are manufactured from a single grid plate comprising for instance perpendicular walls defining the individual light passages. These grids also require a relatively large amount of material for the manufacture, which makes these grids unnecessarily heavy.

Especially the manufacture of low luminance grids often involves a longitudinal distortion due to tensions in the material created during the hardening of said material upon the injection moulding. A high percentage of grids is consequently condemned shortly after production, and later quite a few complaints are made since the grids sometimes warp when aging. Another factor making the manufacture of low luminance grids more expensive is that they must be coated with a mirrorring layer, said coating being previously performed in their total height. Due to the great height of the grids, this metal coating may be rather difficult to carry out since it becomes more and more difficult to make the metal coating penetrate all the way into the modules the higher said modules are. This is due to the fact that the metal emanation can only with difficulty penetrate from the great opening to the bottom adjacent the small opening, whereas practically no metal transfer takes place through the small opening during the rotation of the grids in the metallizing apparatus, when said small opening faces the source of metal emanation. Disclosure of Invention

The object of the present invention is to provide a grid for fluorescent lamp units, whereby the manufacture of such grids requires a lower consumption of material while maintaining the usually recognized shielding angle of the various grids, so that the entire grid is lighter and whereby a new light effect is obtained.

The present invention also provides a low luminance grid, the production cost of which may be essentially reduced by reducing the number of scrappings deriving from distortion tensions created during the hardening upon the injection moulding, and furthermore by reducing the consumption of primary and cover lacquer as well as the other costs in connection with the vacuum metallizing.

This object is achieved by the grid mentioned in the opening paragraph comprising at least two independent, equally high, mutually plane parallel grid members, an upper grid and a lower grid, of which at least one grid member, preferably the upper grid is a shielding grid, said grids being secured adjacent or at predetermined distances from each other by means of retaining means, and whereby the cells in at least one of the grid members are rectangular, polygonal or cylindrical. By a shielding grid, which is also called a light diffusing grid, is meant a grid comprising straight or curved, non-mirrorred wall surfaces transmitting diffused light into the room.

The above manufacture of the individual grid members permits an essential increase of the wall spacing seen in the directions of the grid planes without necessitating that the wall height of each grid member is more than half the height of a usual grid of a corresponding nature, and still maintaining the shielding angle usually aimed at. By such a manufacture the individual walls may simultaneously be made thinner without reducing the strength of the finished grid. As a result an essential total material saving is obtained compared to the known grids. Furthermore new light effects are permitted, inter alia by positioning the grid members at a mutual distance varying from zero mm to for instance the height of more of a grid member. Since the grid comprises a lower and an upper grid having a low height, thinner walls are obtained which lead to a quicker injection moulding.

According to the invention, the grid members may be mutually spaced by means of columns, whereby a surprising, new light effect is obtained, or said grid members may be welded together by means of oblong projections formed on opposing rim surfaces. In the latter case, a sandwich construction is formed possessing the strength properties of laminated parts.

With only two grid members and with the upper grid being a shielding grid comprising walls especially with tapered wall surfaces, and with the narrow topside edge facing the light source, and optionally with curved wall surfaces, and with the lower grid having the same geometrical shape as the upper grid, but with the narrow bottom edge facing away from the light source, it is obtained that the grid members may be manufactured in the same mould so that in addition to the material saving, the production is less expensive. Furthermore, since the mould is not as deep and broad as for a known grid of the same total grid height, a quicker production is ensured.

When it is desired to confect a grid, wherein the grid members are mutually spaced, a particularly solid securing is according to the invention obtained by the bottom and the top of the columns being secured to the grid members in the upper and the lower intersecting portions, respectively, of the walls, and preferably in recesses formed in said intersecting portions.

According to the invention each grid members may be formed integral with a half-column being half as high as said predetermined distance, and that the free end surfaces of the half columns are secured to each other. In this manner the grid members may in a simple manner be manufactured in the same mould provided they have the same geometrical shape.

It is according to the invention preferred that the grid members have the same shape, whereby all the grid members used may comprise either plane or curved wall surfaces with the curvature facing away from the light source. As a result finished grids with a new illuminating effects are obtained. According to a simple embodiment, all the grid members forming part of the grid may thus comprise plane wall surfaces, since the most simple embodiment being easiest and cheapest to produce according to the invention only comprises two identically shaped grid members.

According to the invention the grid members may be of a different type and at least one grid member, preferably the grid facing away from the light source may comprise substantially wedge-shaped walls with tapered and curved wall surfaces with the curvature facing downwards, whereas the remaining grid member (s) may comprise plane wall surfaces. As a result, a light, material-saving grid permitting particular light effects is obtained in a simple manner. The fact that the upper grid is translucent or transparent ensures that said grid to a large extent acts as a light catcher by transmission of light through the walls of said upper grid.

According to the invention, at least one grid member is toned with a colour deviating from white or bright transparent, said shading being produced either by means of an outer coating on the walls or by the optionally transparent plastic material being dyed per se. The use of limpid, transparent, dyed material or by a reflection of the body-colour from the upper grid provides an increase of the transmission of light, said light transmitted or reflected, respectively, being partially reflected from the lower grid to obtain various plays of colours.

By metallizing at least one grid member, preferably the member facing away from the light source, with a mirrorring coating, preferably only the lower grid being mirrorred, whereas the upper grid comprises a non-mirroring coating, a grid is obtained which has an effect between a low luminance grid and a shielding grid. In this manner a pleasant, subdued room light is obtained at the same time as objects situated under the light source are more intensely illuminated. By securing the upper shielding grid to the lower low luminance grid the tensions formed in the lower grid are counter- balanced by means of the upper shielding grid. Since only the low luminance grid is to be metallized in order to mirror, and by virtue of its lower height compared to other low luminance grids, essential amounts of primary and cover lacquers are saved before and af ter metallizing, respectively, as well as the expenses for the vacuum metallizing are essentially reduced at the same time as the metallizing may be carried out in a shorter time owing to the lower height.

The embodiment of the upper grid stated in claim 12 provides the best possible countereffeet to the distortion possibly formed during the manufacture since the upper grid has a slight tendency to curve in an opposite direction. In addition this embodiment ensures that the largest possible opening faces the light source.

The aperture and the dowels mentioned in the characterising clause of claim 13 ensure in a simple manner that the grids are correctly positioned reletive to each other in connection with their mutual securing.

Although the grids may be glued together, which, however, involves environmental problems, it is according to the invention preferred that the individual parts are interconnected by ultrasonic welding. When the opposing rim surfaces of the grid members comprise oblong projections, said projections are flattened during the welding to form a tight assembly. In this manner a use of glue otherwise increasing the price is avoided, said glue besides frequently conflicting with the provisions of local Acts concerning the pollution.

When using certain fireproof materials, the projections of the grids must be interconnectable without employing adhesives. In order to meet this requirement, an embodiment is according to the invention provided, whereby the individual grid members are easily assembled too. The grid members of this embodiment, optionally comprising intermediate columns, are assembled by projections formed on the various parts, and said projections under interference fit being prsssed into corresponding recesses in the corresponding parts. These projections and recesses may optionally be formed to provide a snaplock-like engagement so as to ensure a reliable intersecuring of said parts.

When each grid member is manufactured by means of a plurality of rectangular grid elements with a chosen number of cells (light passages), said elements through mutual securing being confected into a grid member, it is according to the invention preferred that the grid elements of one lower grid are staggered relative to the elements of an upper grid, whereby the warping or distortion of the grids into an arch upon the assembling is counteracted in such a manner that a lower scrapping percentage is achieved.

Brief Description of Drawing

Various examples of embodiments of the invention will be described below with reference to the accompanying drawing, in which

Fig. 1 is a side sectional view of a grid according to the invention.

Fig. 2 is a sectional view taken along the line A-A of Fig. 1,

Fig. 3 is an axiometric illustration of the portion C of Fig. 2,

Fig. 4 is a sectional view through a second embodimentof the grid according to the invention corresponding to the sectional view of Fig. 1, Fig. 5 is a diagrammatic, top view of a grid with hexagonal cells.

Fig. 6 is a sectional view of a second embodiment of a grid according to the invention corresponding to the sectional view of Fig. 1,

Figs. 7 and 8 are sectional views corresponding to Fig. 1 and Fig. 2, respectively, of a known shielding grid,

Fig. 9 is a sectional view of a third embodiment of a grid according to the invention,

Fig. 10 illsutrates a grid member for use in connection with the grid of Fig. 9, seen towards the broad rim surface of the grid member,

Fig. 11 is on an enlarged scale a sectional, fractional view through a low luminance grid according to the invention, taken along the line D-D of Fig. 12,

Fig. 12 is on another scale a top view of a lower grid for the low luminance grid of Fig. 11, and

Fig. 13 is a sectional view taken along the line E-E og Fig. 2.

Mode for Carrying Out the Invention

An embodiment of the light grid according to the invention is illustrated in Figs. 1-3. This grid comprises two principally equal grid members 1, 2, the light passages or cells 3 of which are defined by walls 4, 5 and6, 7, respectively, perpendicular to each other and comprising plane wall surfaces in such a manner that each grid member forms a shielding grid. The grid members are mutually spaced by means of retaining means in the form of columns 8 preferably located in all intersecting portions. These columns 8 may be moulded integrally with one grid member and at the opposite end comprise a projection (not shown) engaging a recess (not shown) in the intersecting portion of the other grid member. A light source 9 is indicated by a dotted line above the grid of Fig. 1. The grids are interconnected by interference fit or ultrasonis welding of the columns at the contact spots of the grid in question. Glue may, however, also be employed, but glue may involve environmental problems. As an alternative, snap-lock-like means may also be used, but they raise the price of the production mould.

According to an embodiment, the two grids are manufactured identically with a half-column located on each grid. These half-columns comprise plane wall surfaces and are assembled along the line A-A of Fig. 1, the projections and recesses mentioned not being absolutely necessary for the manufacture of the grid, but they can facilitate the accurate positioning of the grid members relative to each other. This positioning may be guided by means of other mechanical means known per se, but without a permanent connection with the grid members.

It is advantageous to use spacers in the form of vertical columns 8. The bottom 10 and the top 11 of these columns are secured to the walls 6, 7 of the upper rim surface 12 of the lower grid member of the lower grid 1 and to the lower rim surface 13 of the walls 4, 5 of the upper grid member or the upper grid 2 . The bottom 10 and the top 11 of the columns are furthermore secured to the grids in the upper and lower intersecting portions 14, respectively, of the walls 4, 5, 6, 7. Another embodiment of the grid according to the invention is illustrated in Fig. 4. The upper grid 2 of this embodiment corresponds to the grid of Fig. 1, whereas the surfaces of the walls 16, 17 of the lower grid 15 are substantially tapered and may be curved as illustrated and optionally mirrorred. The curvature may for instance be parabolic or as illustrated be a length of a circular arc with a radius R. As illustrated in Fig. 4 it is for the reasons of illumination preferred that the lower rims 18 of the walls are rounded. The grid members 2, 15 of this grid are also mutually spaced by means of the columns 8 as described above.

Fig. 5 illustrates diagrammatically that it is not nercessary that the walls are perpendicular to each other, but the walls 14 of this embodiment are shaped in such a manner that hexagonal cells or light passages are formed. The columns 8 of this embodiment are preferably located in the intersecting portions 21 of three walls 19. Many ohter embodiments of the grid according to the invention are possible. Each grid member may for instance comprise a grid member known per se comprising walls perpendicular to each other, and whereby a cylindrical light passage is situated in each light passage or cell. Each of these embodiments of the grid members provides its particular light effect or shows when illuminated a characteristic appearance. These embodiments are not described in greater detail.

Fig. 6 illustrates an additional embodiment of the invention, whereby an intermediate grid 22 is coupled between the lower grid 1 and the upper grid 2. This intermediate grid is spaced from the two other grids by means of the columns 8, 23. A grid of this type and manufactured as a shielding grid with plane wall surfaces provides an additional material saving at the manufacture of the grid. However, such a grid requires somewhat higher fluorescent lamp units than the grid illustrated in Figs. 1-3.

Best Mode for Carrying out the Invention.

The preferred embodiment is illustrated in Figs. 9 and 10. This embodiment comprises two like grid members 15, 15', the wall surfaces 16, 17 of which are substantially tapered and curved, said surfaces being tightly welded together with the broad rim surfaces 24 of the walls abutting each other. The retaining means is present in the form of oblong projections 25 extending at the middle of the rim surface 24. The height of these projections is between 0.1 and 0.4 mm, and preferably about 0.2 mm. At the ultrasonic welding these projections are flattened in such a manner that a tight, reliable connection between the grid members 15, 15' is obtained.

Due to the thin shape of the walls, such a grid possesses a large light incidence opening compared to the prior art, so that a great transmission of light is obtained in comparison to said prior art.

An additional embodiment of a low luminance grid according to the invention is illustrated in Figs. 11-12. This low luminance grid comprises a lower grid 31 and an upper grid 32, and is as shown located under a light source 33 indicated by a dotted line and usually being one or several fluorescent tubes.

The lower grid 31 comprises a first and a second pair of walls 34, 35 perpendicular to each other. These walls 34, 35 form light passages of a desired width, e.g. of about 12 x 12 mm. Many other sizes of openings are, however, also possible, e.g. 200 x 200 mm. The height of the walls depend on the established width and in connection with a width of 12 x 12 mm, it is consequently about 6 to 10 mm and may e.g. be 6.5 mm from the top surface. At the bottom, these walls 34, 35 are rounded, which provides a better distribution of the lacquer in connection with the metallizing. In addition, the tendency to formation of drops is not as great as with sharp rims,whereby the risk of brown-colouring and breaking off of lacquer is simultaneously avoided. In a manner known per se, the walls 34, 35 comprise curved wall surfaces 37 having a radius r in the present embodiment, said radius being determined by the requirements of the illumination. The wall surfaces may also be parabolic in section.

At the centre of the intersecting portions 38 of the walls 34, 35, a dowel 39 extending towards the light source is located. In the present embodiment, this dowel comprises either a circumferential bead-like projection 48 or several bead-like projections not shown and extending circumferentially. According to another embodiment, the dowels may be made without the projections, cf. also the following description of the assembling of the low luminance grid according to the invention.

The top surface 40 of the walls of the lower grid has a predetermined width b, which in response to the selected grid height and width of the light opening may be in the range of 1.5 to 12 mm, and is preferably between 3 to 4 mm, and is for instance 3.4 mm.

The upper grid 32 also comprises a first and a second pair of parallel walls 41, 42 perpendicular to each other and comprising plane wall surfaces 43. The height of the walls of the upper grid depends on the walls of the lower grid. The light opening formed by the walls 41, 42 is in principle of the same size as the light opening formed by the walls 34, 35 of the lower grid, since the bottom surface 44 of the walls 41, 42 of the upper grid may be of the same width b as the top surface 40 of the walls 34, 35 of the lower grid. As illustrated, the walls of the upper grid may be tapered. An aperture 45 is formed in the bottom surface 44 of the two walls 41, 42 of the upper grid in the intersecting portions not shown. The shape of this aperture 45 is identical with the shape of the dowel 39, which means that the aperture may comprise a circumferential recess 46 or recesses partially extending along the circumference, or the aperture may comprise smooth walls.

While the lower grid 21 is metallized prior to the assembling so that all its surfaces are coated with a mirrorring layer, the upper grid 32 is manufactured of a translucent or transmitting plastics, thereby ensuring the largest possible light passage through the entire grid.

Following the metallizing of the lower grid 31, the upper grid 32 is pressed downwards over the lower grid in such a manner that the bottom surface 44 of the upper grid contacts the top surface 40 of the lower grid. As a result, the dowels 39 contact the wall surfaces of the apertures 45. When the dowels are provided with the circumferential projections 48, a snap-lock-like engagement in the corresponding recesses 46 is provided. When the dowels 39 and the apertures 45 comprise smooth wall surfaces, the contacting surfaces are welded together by means of ultrasonic welding. The top surface 40 and the bottom surface 44 may also be welded together for the purpose of a close contact therebetween. In this manner the grids reinforce each other and counteract due to their complementary shape the formation of possible distortions in the finished grid. The dowels and the apertures may optionally be omitted.

The purpose of the upper grid in the above embodiment of the low luminance grid according to the invention is to assemble the light from the light source prior to the further transmission thereof through the lower grid. This assembling of light is improved by the upper grid being injection moulded in translucent, transparent or opale plastics, whereas the lower grid transmits the light further in a manner known per se to obtain a controlled directional flow of light.

As mentioned above, the height of a low luminance grid is often a problem when metallizing at a vacuum. This is due to the fact that it may be difficult to transfer the metal coating sufficiently into the modules the higher said modules are, the metal emanation having difficulty in being carried from the large opening to the bottom at the small opening, whereas practically no metal transfer takes place through the small opening. According to the invention, only the lower grid is metallized, whereby the height is essentially reduced. In addition, it is even possible to metallize two opposed lower grids, whereby a double amount of vacuum metallized light grids may be manufactured and the processing is consequently reduced to almost half the expense in comparison with known grids. When assembling the lower and the upper grid, these grids may be staggered so as to constitute a stronger light grid at the confecting of larger grids, especially since the assembling of the grid members and the lower and the upper grip is preferably performed by ultrasonic welding. In this manner the use of the known glues is avoided, many of these known glues conflicting with the provisions of the local Act on pollution. For the manufacture of grids of fireproof materials, it is an additional requirement that the upper and the lower grids can be interlocked by means of a snap-lock effect.

In all the above embodiments, at least one grid member may be toned in a colour deviating from white or a bright transparent. This toning is either performed by means of an outer coating on the wall or by the optionally transparent plastic material being dyed per se. Correspondingly, one of the grid members, preferably the lower grid, may be metallized with a mirrorring coating, whereby a combination of an appropriate dyeing of the upper grid and a second dyeing or a mirrorred coating of the lower grid provdes various new and surprising light effects.

It is preferred to manufacture each grid member by means of a plurality of rectangular elements, parts thereof appearing from Figs. 10 and 12. Each element has a predetermined number of cells, e.g. 16 or 64. At the interconnecting procedure, these elements are assembled along outer defining surfaces 47 into particular grid members. By this procedure smaller and consequently less expensive moulds may be used. At the assembling of such elements (not shown), it is preferred to displace the elements of a lower grid relative to the elements of an upper grid in such a manner that an element of the upper grid accurately overlaps the half of two elements of a lower grid. Elements of the upper grid of half the width of a complete element may then be secured at the end of the grid. In this manner the distortion are counteracted, which have a tendency to be formed in moulded grids on account of tensions established in the grids during the cooling after the moulding. This securing may be performed by means of glue, but it is preferred to secure them to each other by ultrasonic welding. These distortions are counteracted by location grids having a tendency to bend oppositely on top of each other. As a result, the tool expenses and the scrapping percentage are reduced, and the entire processing is less expensive.

For comparison purposes. Figs. 7 and 8 illustrate a generally known low luminance grid. Since this known grid is of an essentially greater wall height than each grid member, the walls thereof are made with a greater thickness than the wall thickness of the grids according to the invention. Furthermore, these walls must be located closer to each other in order to obtain the desired shielding angle α than the finished grids according to the invention, cf. Figs. 1, 6, and 7. This implies that an essentially greater amount of material is used for the known grid than for the grid according to the invention, which makes the production unneccessarily expensive. The finished known grid furthermore has a greater weight than the grid according to the invention.

Although both the lower and the upper grids shown in the drawings are shown as having rectangular or hexagonal cells , other geometrical cell shapes such as other polygonal cells or circular or oval cells may be used.

The advantages of the grid according to the invention can be summarized as follows:

- A saving of material is achieved since the walls of the grid members preferably made of plastics may be made considerably thinner than corresponding walls of grids made of plastics without weakening the grids, and since a number of calls can be omitted while maintaining the same shielding angle α, each celle or light passage may be made relatively larger.

- A lower height of both the upper and the lower grid, which involves less tool expenses and a quicker injection moulding of blanks. A slight difference exists in the thickness of the material in the entire height of the walls, which involves a lower degree of distortion in the longitudinal direction of the grid.

- The production is somewhat more simple since the processing tools due to the lower height of the grid members are easier to manufacture.

- A combination grid, whereby the lower grid member is shaped with curved surfaces to produce a low luminance grid, is less expensive to manufacture since only the lower grid needs to be mirrorred, whereby considerable expenses are saved in connection with the mirrorring, and this mirrorring may furthermore be more efficient on account of the low height of the grid.

New light effects are obtainable by means of the space between the grids and by varying the combination of shielding grids and low luminance grids and the toning of each grid member.

- An increased light passage is obtained due to the greater cells and the smaller wall thickness.

The lower and the upper grid member may be staggered relative to each other in such a manner that a strong light grid is provided when manufacturing bigger light grids.

The total weight is lower. By manufacturing a low luminance grid, the consumption of lacquer for the primary and the body-lacquer after the metallizing is reduced.

By manufacturing a low luminance grid, the expenses in connection with the vacuum metallizing are considerably reduced.

The assembling of the lower and the upper grid and the finished assembly may be performed by ultrasonic welding, glueing and the environmental problems are avoided. The ultrasonic welding is quicker and less expensive to perform.

A light grid involving a small consumption of energy compared to the amount of light transmitted.

A light grid permitting various decorative embodiments.

Beyond the above embodiments, many variations may be performed within the scope of the invention, a lower grid of the shape shown in Fig. 5 may for instance be made parabolic or provided with circular wall surfaces or as a multi-layer grid. Furthermore, the lower grid member 1 of the grid illustrated in Fig. 6 and/or the intermediate grid 17 and/or the upper grid member 2 may be manufactured as a low luminance grid with curved wall surfaces. Each embodiment provides a new light effect.

The bottom surface of the upper grid may be made narrower or broader than the surface of the low grid. Thus it is obvious that the projection- and aperture connection may be replaced by other connecting means such as for instance grooves and tongues.

Claims

Claims:

1. A grid for fluorescent lamp units preferably for ceiling or wall illumination and comprising a plurality of cells (36) defined by walls (4, 5, 6, 7, 16, 17, 19, 34, 35, 41, 42) of an appropriate height and located at regular intervals permitting light to flow through said cells, c h a r a c t e r i s e d in that the grid comprises at least two independent, equally high, mutually plane parallel grid members (1, 2, 15, 15', 22, 31, 32), an upper grid and a lower grid, of which at least one grid member, preferably the upper grid (2, 32) is a shielding grid, said grids being secured adjacent or at predetermined distances from each other by means of retaining means (8, 25, 39, 45), and whereby the cells in at least one of the grid members are rectangular, polygonal or cylindrical.

2. A grid as claimed in claim 1, c h a r a c t e r i s e d in that the retaining means are oblong projections (25) or vertical columns (8), the bottom (10) and top (11), respectively, of which are permanently connected to the upper rim surface (12) of the walls (6, 7, 16, 17, 19) of the lower grid (1, 15, 22) and to the lower rim surface (13), respectively, of the walls (4, 5, 16, 17) of the upper grid (2, 15', 17).

3. A grid as claimed in claim 2, c h a r a c t e r i s e d in that the projections (25) are formed as short, oblong projections on the rim surfaces (24).

4. A grid as claimed in claim 2 or 3, c h a r a c t e r i s e d by comprising only two grid members (15, 15'), and by the upper grid (15') being a shielding grid comprising walls (16, 17) especially with mutually tapering wall surfaces and with the narrow top side edge facing the light source (9), and optionally curved wall surfaces, whereas the lower grid (15) is of the same geometrical shape as the upper grid (15'), but whereby the narrow bottom edge faces away from the light source (9).

5. A grid as claimed in claim 2, c h a r a c t e r i s e d in that the bottom (10) and the top (11) of the columns (8) are secured to the grid members in the upper and the lower intersecting portions (14, 21), respectively, of the walls (4, 5, 6, 7, 16, 17), and preferably in recesses formed in said intersecting portions.

6. A grid as claimed in claim 2, c h a r a c t e r i s e d in that each grid member (1, 2, 15) is formed integral with a half-column being half as high as said predetermined distance, and that the free end surfaces of the half-columns are secured to each other.

7. A grid as claimed in claim 1 and one of the claims 5 or 6, c h a r a c t e r i s e d in that the walls (4, 5, 6, 7, 16, 17, 19) in all the grid members (1, 2, 17) are of the same cross section, and in case the wall surfaces are tapered and optionally comprise curved wall surfaces, with the broad portion facing the light source (9).

8. A grid as claimed in claim 1 and one or several of the claims 2, 5, and 6, c h a r a c t e r i s e d in that the grid members (2, 15) are of different shapes, and that at least one grid member (15), preferably the grid facing away from the light source (9), comprises walls (16, 17) substantially wedge-shaped in cross section and with curved wall surfaces, said curvature fac¬ing downwards, whereas the remaining grid member (s) comprise plane wall surfaces.

9. A grid as claimed in one or more of the preceding claims, c h a r a c t e r i s e d in that the upper grid (15, 15', 32) is made of opal or transparent plastics.

10. A grid as claimed in one or more of the preceding claims, c h a r a c t e r i s e d in that at least one grid member is toned with a colour deviating from white or bright transparent, said shading being produced either by means of an outer coating on the walls or by the optionally transparent plastic material being dyed per se.

11. A grid as claimed in one or more of the preceding claims, c h a r a c t e r i s e d in that at least one grid member is metallized with a mirrorring coating, preferably only the lower grid being mirrorred whereas the upper grid comprises a non-mirrorring coating.

12. A grid as claimed in claim 1 and claims 10 and 11, and whereby each lower and upper grid (31, 32) comprises a first and a second pair of parallel walls (34, 35; 41, 42) located directly above and perpendicular to each other, said walls forming light passages (36) of a desired height and width, and whereby the walls (34, 35) of the lower grid (31) are wedge-shaped with the tapered end of the wedge turning downwards and comprise a substantially plane top surface (10), and preferably curved mirrorring wall surfaces, c h a r a c t e r i s e d in that the walls (41, 42) of the upper grid (32) formed as a shielding grid comprise plane parallel walls or are wedge-shaped with plane wall surfaces and are broadest at the bottom surface (44) facing away from the light source (33), said bottom surface preferably being of the same width (b) as the top surface (40) of the walls (34, 35) of the lower grids.

13. A low luminance grid as claimed in claim 1, 10, 11 or 12, c h a r a c t e r i s e d in that apertures (45) are formed in the intersecting portions of the two sets of walls of the upper grid (32) in the bottom surface (44) of said upper grid (32), said apertures engaging corresponding dowels (39) formed integral with the walls of the lower grid (31) in the intersecting portions (38) of said walls (34, 35).

14. A low luminance grid as claimed in claim 12, c h a r a c t e r i s e d in that the dowels comprise circumferential projections (48) engaging corresponding recesses (46) in the apertures (45).

15. A grid as claimed in claim 1 and one or more of the claims 2 to 13, c h a r a c t e r i s e d in that the individual parts (1, 2, 8, 15, 15', 23, 25) are interconnected by ultrasonic welding.

16. A grid as claimed in claim 1 and one or more of the claims 2 to 10, c h a r a c t e r i s e d in that the grid members (1, 2, 15, 15') optionally comprising intermediate, independent columns (8) are assembled by projections formed thereon and under interference fit being pressed into corresponding recesses in the individual parts.

17. A grid as claimed in claim 1 and one or more of the claims 2 to 12, and whereby each grid member is manufactured by means of a plurality of rectangular grid elements with a chosen number of cells, said elements through mutual securing being confected into a grid member, c h a r a c t e r i s e d in that the grid elements of a lower grid member (1, 15, 22) are staggered relative to the grid elements of an upper grid member (2, 15', 17).