The present invention relates to an improvement in fixtures for luminous tubes or bulbs, and more specifically an improved version of the transverse lamellas or fins in the light shielding grid of the fixture.
In an early stage it was realized that ceiling-mounted illumination with luminous bulbs could be provided with an opportune and comfortable design or mode of operation by fitting the fixture with a light shielding grid which provides a downward directing of the light by shielding and reflections. In their simplest form, such grid devices will, in addition to side and end reflectors intended for reflecting light mainly downward, be equipped with simple crossbar-like transverse fins in the form of vertically upright plates just below the luminous bulb or bulbs, mounted in a suitable number between the side reflectors, and with number, height and interval distance adapted for maximum allowable light scatter angle, maximum desirable construction height of the fixture etc.
It was also soon realized that the lighting conditions below a fixture could be improved further by introducing an improved type of transverse fins, namely (in cross section) Y-or V-shaped fins with concavely curved outer sides, often with parabolic type of curvature. Using such a design, improved darkening or shielding conditions are achieved, even though the light output or efficiency will be somewhat lower due to loss "inside" the fins or lamellas.
European patent application no. 138.747 discloses an example of such V-shaped transverse fins. In addition, the fins shown in said European application are designed with a three-dimensional curvature in the reflecting surfaces in order to improve the shielding conditions regarding obliquely reflected light rays.
Curved and reflecting fins are also known from German Gebrauchsmuster DE-U-1984108, however, the grid is in this case a two-dimensional grid consisting of both transverse and longitudinal fins for dividing the light output into small "cells". Particularly in the embodiment regarding curved fins, the effect in said Gebrauchsmuster is explicitly stated to be that of creating light "funnels" in a downward direction. The present invention is, however, directed to providing a one-dimensional grid fixture allowing a much larger part of the light to escape down into the room.
Other variants have been developed, and it is referred to figures 2, 3 and 4 which show previously known shapes of transverse lamellas. Fig. 2 corresponds approximately to the above mentioned cross-sectional shape. Fig. 3 shows a closed top part of the V-fin, for achieving a reflection back again of the light, which then entails a higher light yield from the fixture due to inter-reflections which pass the upward reflected light from the fins, down again. However, some loss still exists. The structure shown in fig. 4 provides a good increase of the light yield, but this implies the disadvantage of increasing the fixture construction height with a height difference of H2-H.
The purpose of the present invention is to provide a fixture with transverse lamellas or fins which results in a corresponding increase in the light yield as the last mentioned variant, however without increasing the construction height in comparison with the variants of fig. 2 and 3. Said purpose is fulfilled by providing a luminous bulb fixture as defined in the patent claims.
A closer description of the invention shall be given in the following, referring to the embodiment example appearing from fig. 5 and 6,
It should first be noted that the following description for simplicity reasons merely mentions horizontal mounting of the fixture, that is the usual ceiling mounting, however, it is also of course possible with other mounting conditions (slanting ceilings, or even on walls). The patent claims have been worded in a manner which is independent of horizontal mounting of the luminous bulb, i.e. independent of fixture position.
Fig. 1 shows a ceiling mounted fixture with one single luminous tube 4. The fixture is equipped with side reflectors 1, end reflectors 2 and quite simple plate-shaped transverse fins 3 for shielding and downward directing of the light from the luminous tube or bulb. As a starting point, here the height of each fin or lamella 3, as well as the distance between fins, determine the maximum angle with the vertical direction for escaping light rays in the case of a direct reflection, however multiple reflections imply a much wider scatter angle and poorer control of the darkening conditions.
In figs. 2, 3 and 4 which have been mentioned above, reference numeral 5 refers to more advanced designs of fins or lamellas, where the result is a poorer light yield than in the first case, however in return, better control of the shielding angle is achieved, and consequently more correct and comfortable illumination conditions. As previously mentioned, the solution in fig. 4 gives the better light yield, but the problem in this case is the increased construction height, which is usually not desirable.
In fig. 5 is shown a lamella example in accordance with the present invention. The same external geometry as in the V-shapes in figs. 2, 3 and 4 has been retained, i.e. preferably a parabolic curvature type for the the outer surfaces 7. However, the previous "V"-lamella has now been spilt into two single fins 6 in a mirror symmetrical relation, in such a manner that light can pass also "inside" or "through" the pair of fins 6-6. On the inside, surfaces 8 and 9 are of a reflecting type in the same manner as the outer surfaces 7. The upper and lower edges are shown respectively with reference numerals 10 and 11. 12 indicates an edge line (into the paper plane) separating the two inner surfaces 8 and 9. An imaginary symmetry plane in the center is indicated by reference numeral 13, and is positioned perpendicularly to the luminous tube or bulb. Reference numeral 14 indicates the axis of the luminous bulb.
The inner surfaces 8 are either flat or shaped with a slightly convex curvature type. Preferably the lower inner surfaces 9 have the same curvature type as the outer surfaces 7, however in a re-scaled, i.e. reduced version, so that the radius of curvature varies in the same manner, but is scaled down with a fixed factor.
The upper inner surface 8 follows to a larger or smaller extent the curve of the lamella outside 7, however deviates slowly in a downward direction, either by a somewhat different curvature, or by being a flat surface, so that the "inversely curved" lower inner surface 9 starts from an edge 12 and curves back to the lower end edge 11.
The distance between the single fins 6 in a fin pair is adjusted in such a manner that the same maximum exit angle is achieved also for light passing through said pair, as for light passing either directly or via reflections between the pairs. This is achieved by a proper choice of dimensions, as will be dealt with in more detail below.
The splitting up of tranverse lamellas of the V-type in two parts, so that light passes also "through" the lamella, either directly or via reflections, as indicated in the present invention, increases the efficiency of the fixture without renouncing the requirements for technical illumination characteristics.
Fig. 6 shows examples of oblique ray passage through a grid of transverse lamellas 6 in accordance with the present invention. If a maximum light exit angle α with the vertical direction is desirable, and the construction height implies a maximum lamella height H, the new lamellas or fins are placed with a distance from one lamella pair to the next pair equal to B, so that tan α = B′/H where B′ is the horizontal distance from the top of one lamella or fin to the lower edge of the closest lamella or fin in the adjacent pair of fins. With the curvature type in question, it is then ensured that any light ray in the space between pairs is reflected downward and out from the grid with an angle equal to or smaller than α.
Regarding the light passage "inside" a pair of fins, the preferred solution ensures, with regard to the lower reflection surfaces 9, that the same maximum exit angle α is obtained, and at the same time the total light yield is increased substantially in relation to the previously known solutions.
In order to achieve the same maximum angle α, the distance A is adjusted in the preferred embodiment with similar surfaces 9 as the surfaces 7, in such a manner that the ratio A′/h, h being the height from the lower edge 11 to the edge 12, and A′ being the horizontal distance between lower edge 11 and inside edge 12 for two respective lamellas in a pair, equals tan α.
Thus, in this case, the two geometrical figures marked S-S-S-S and L-L-L-L in fig. 6, will be similar.
Any light ray, directly or indirectly from the light source, is thus reflected from surfaces 7 or 9 with an angle β which is smaller than or equal to α.