US2882389A

US2882389A - Lighting fitting for road illumination

Info

Publication number: US2882389A
Application number: US516874A
Authority: US
Inventors: Rijnders Johannes
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1954-06-30
Filing date: 1955-06-21
Publication date: 1959-04-14
Anticipated expiration: 1976-04-14

Description

Ayril 14, 1959 J. RIJNDERS 2,

LIGHTING FITTING FOR ROAD ILLUMINATION Filed'June 21, 1955 INVENTQR H\ JOHANNES RIJNDERS 53.1 v BY AGENT United States Patent LIGHTIN G FITTING FOR ROAD ELIMINATION Johannes Rijnders, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application June 21, 1955, Serial No. 516,874

1 Claims priority, application Netherlands June 30, 1954 2 Claims. (Cl. 240-25) A lighting fitting comprising one or more fluorescent tubes as a source of light is known for street and road illumination. It has been found that road users, more particularly car-drivers, are sometimes dazzled by the sources of light used in these fittings. In general, a lighting fitting is considered to be troublesome to the road users, if this fitting radiates light in directions which are at an angle of less than to to the horizontal line. The dazzling effect of such lighting fittings could be eliminated 'by providing a hood above the source of light, the free end of this hood being provided with a screen projecting downwards, which screen had to be proportioned to be such that the radiation of light in the zone referred to above is suppressed. This construction, however, has a limitation in that a lighting fitting thus constructed is comparatively bulky. This is particularly the case, if a plurality of these sources of light are provided in a fitting in positions one below the other.

The present invention has for its object to provide a solution for this problem, in which the disadvantage stated above is obviated.

The lighting fitting according to the invention has the feature that the elongated, cylindrical discharge lamp cooperates as a source of light, with a cylindrical, convex lens, the focal line of which, as is also the case with the source of light, extends at least substantially horizontally. This lens is arranged with respect to the source of light in a position such that, viewed in sections at right angles to the focal line of the lens, the distance between the bottom part of the source of light and the optical centre of the lens corresponds at least substantially to the focal distance of the lens in these sectional areas and, also viewed in these sectional areas, the line which is at least substantially tangential to the bottom part of the source of light and which passes through the optical centre of the lens, is at an angle of 10 to 30 to the horizontal line. The optical axis of the lens coincides preferably with the said tangential line.

With the sources of light employed in the lighting fitting according to the invention the light radiating part thereof has a diameter, which corresponds at least substantially to the diameter of the bulb of this source of light. Thus, with a so-called fluorescent lamp, the bulb wall of the tube operates as a source of light. With a low-pressure sodium-vapour discharge tube the outer side of the discharge tube is located in close proximity of the inner side of the bulb. Such sources of light deviate, consequently, as far as the shape of the source of light proper is concerned completely from an electric incandescent lamp having a bulb of clear glass, in which an incandescent body is extended .in the direction of length. With this source of light, the light radiating member is not cylindrical, but linear.

The aforesaid cylindrical sources of light are suitable for the purpose aimed at particularly since, when housing this kind of sources of light in the fitting, it is sufiicient to position accurately one of the surfaces of the bulb wall, which, is thus. employed as an adjusting member.

1 three cylindrical, elongated sources of light, arranged one Patented Apr. 14, 1959 Owing to the fact that with the lighting fitting according to the invention, viewed in sectional areas taken at right angles to the focal line, the line Which is substantially tangential to the bottom part of the source of light and which passes through the optical centre of the lens, is an angle of 10 to 30 (which depends upon the desired position of the light-dark boundary) to the horizon tal line, it is possible to construct the lighting fitting according to the invention, which is extremely simple in itself, in a manner such that it does not give rise to dazzling for the road users. With this lighting fitting there is a very sharp and abrupt transition from light to darkness owing to the predetermined angle, for which reason this lighting fitting is extremely suitable for the illumination of streets and roads. Although it is not strictly necessary for a satisfactory operation of the lighting fitting, it is desirable, in order to obtain an optimum effect from the lens, that the line passing through the optical centre and being at least substantially tangential to the bottom part of the associated source of light, i.e. viewed in sectional areas taken at right angles to the focal line of the lens, should coincide with the optical axis of this lens.

In accordance with a further preferred embodiment of a lighting fitting according to the invention such a cylindrical, convex lens is provided one on each side of the source of light. Thus, a simple lighting fitting of little volume is obtained, the light being radiated to two sides without causing the dazzling effects as referred to above.

If, for example, with respect to the height of suspension or to the luminous output of each source of light, it would appear that one source of light for one lighting fitting does not sufiice, this lighting fitting may, in accordance with a further preferred embodiment of the invention, be arranged in a simple manner to accommodate a plurality of elongated, cylindrical sources of light arranged one below the other in substantially horizontal positions. With this embodiment, in which each source of light is associated With a single lens or with two lenses provided one on each side of this light source, these lenses having a cylindrical, convex shape, the angle, viewed in sectional areas taken at right angles to the direction ofnot only with the associated lens but also with the adja-' cent lenses, the light emanating from the source of light and concentrated by these neighbouring lenses will not have a dazzling effect. In order to obtain this result, the lighting fitting need not comprise intermediate partitions to screen off certain rays of light.

With lighting fittings, which comprise a plurality of cylindrical sources of light arranged one below the other, it is common practice to envelope all these sources of light in common in a transparent envelope, which may be made from a synthetic substance, for example glass. By means of a suitable shape of the mould in which such an envelope is made it may be ensured that during the manufacture of such an envelope the cylindrical convex lenses are at the same time provided thereon.

The invention will be described ore full with reference to the drawing.

Fig. 1 illustrates an arrangement including a cylindrical, elongated source of light with respect to an associated cylindrical convex lens, in a sectional view taken at right angles to the focal line of this lens and at right angles to the direction of length of this source of light.

Fig. 2. is a sectional view of a lighting fitting comprising below the other, the transparent envelope of the fitting being provided with cylindrical lenses.

Fig. 3 is a front view of the complete lighting fitting, viewed by a road user looking in the direction of length of the road.

Referring now to Fig. 1, reference numeral 1 designates the cross sectional area of the fluorescent lamp, the bulb surface of which operates as the light radiating member. This source of light 1 co-operates with a cylindrical lens 2, indicated by a straight line. The focal line of this lens 2 intersects the plane of the drawing at A; this line extends parallel to the direction of length of the source of light 1. This focal line and the source of light 1 occupy horizontal positions in the operational position of the lighting fitting. References BC designate the optical axis of the sectional area of the lens 2 taken in the plane of the drawing; at D is located the optical centre of this sectional area of the lens 2. The source of light 1 is arranged with respect to the lens 2 in a position such that the tangential line E-F to the bottom part of the source of light 1 and passing through the optical centre D of the sectional area of the lens 2 shown is at an angle a, in this case of 15, to the horizontal optical axis BC of the lens 2. Moreover, the tangential point G of the line BF to the outer surface of the source of light 1 is spaced apart by a distance p from the optical centre D of the lens 2, this distance p corresponding at least approximately to the focal distance i of the sectional area of the lens 2. As a result of this arrangement, the bottom part of the source of light 1, will produce a light beam, indicated by the light rays I and II, owing to the efiect of the lens 2, this beam being at least substantially parallel to the line BF. Parts of the source of light which occupy higher positions will radiate light rays which, subsequent to their passage through the lens 2 are concentrated to form light beams, the main directions of which are at gradually larger angles than the angle a to the horizontal line. This is illustrated in Fig. 1 by means of the light ray III. Consequently, the arrangement shown results in that a very sharp boundary of the radiated light is obtained at an angle a, which, consequently, has a value of 15 in this case, so that this lighting fitting will not have a dazzling efiect.

From Fig. 1 it appears, moreover, that just the cylindrical source of light is particularly suitable for the purpose aimed at. If, for example, the source of light is constituted by a fluorescent lamp or by a low-pressure sodium vapour discharge tube, the bottom part of the bulb of the source of light may be positioned very accurately with respect to the line BF or H-I respectively, which is required to obtain the desired abrupt transition from light to darkness at a predetermined angle. As is shown in Fig. 1, it is practically indifferent whether the lines E-F or H] respectively are tangential to the circumference of the circle 1 or 3 respectively or Whether they pass through the lower point of these circles. It is furthermore in practice fairly indifierent whether these lines are adjusted to the outer side or to the inner side of the wall of the bulb of the source of light. It is essential, however, that the bulb of the source of light in the direction of length and the focal line of the cylindrical lens should both be straight. This has the result that light rays are radiated within the angle, which is critical as far as dazzling is concerned and which is des ignated in Fig. 2 by b.

With the embodiment shown in Fig. 2, the lighting fitting comprises three sources of

light

10, 11 and 12, which are arranged horizontally one below the other. They are held in these positions by the frame 13 (shown diagrammatically), which also supports the associated electrical auxiliary members. This frame itself is supported from a hood 14, in which also the

reflectors

15 and 16 are housed. To the flanges 17 and 18 of the reflectors 1S and 16 is secured the transparent envelope 19 of synthetic substance, for example, glass, by means of bolts of the source of light 12, this tangential line R-Q being at an angle 0 having a value of 10, to the horizontal line S-T. This means that the light emanating from the bottom part R of the source of light, after having been concentrated into a beam by the lens 12 is deformed into a parallel beam of which two rays VIII and IX are indicated, it being assumed that the distance -RQ is at least substantially equal to the focal distance of the lens 12". In a similar manner the bottom parts of the sources of

light

10 and 11 radiate parallel light beams, subsequent to the concentration into a beam by the lenses 10 and 11 (a few rays of these beams are designated by X and XI and X11 and XIII respectively). A similar effect is obtained by the provision of the

lenses

10, 11 and 11 It will be obvious that since the centre lines of these beams are, all of them, at an angle c, having a value of 10, to the horizontal line, these beams and hence the lighting fitting shown cannot give rise to dazzling.

As is evident from Fig. 2, there is a possibility that light rays from the sources of

light

12 and 11 should find their way to the

higher lenses

11 and 10 Thus light rays directed upwards can yet emerge from the light ing fitting. These light rays, of which a few are designated by XIV and XV, XVI and XVII respectively, can, however, not give rise to dazzling, since this lighting fitting is always suspended at a height a few metres over the road surface, i.e. above the level of the eye, so that such rays, which are directed upwards, can never reach the eyes of a road user. To this end it is required that, as is indicated for the lens 11*, the tangential lines passing through the optical centre U and tangential to the parts of the adjacent sources of

light

11 and 12, which face one another, i.e. the lines UV and UW, should be at an angle d, which is at least equal to the angle 0 and which is 10 in this case.

As is evident from this figure, the invention provides the possibility to obtain a non-dazzling lighting fitting of very small size. If the diameter 2 of the sources of light is, for example, 40 mms. and if the focal distances of the lenses 10 10 11 11 and 12, 12 are for example, mms., the lighting fitting obtained has an envelope of about 200 mms. in height and also 200 mms. in width.

Fig. 3 is a front view of this lighting fitting, reference numerals 20, 21 and 22 designate the cylindrical, convex lenses and 23 designates the hood. By means of the extension 24, this hood is secured to a lighting post 25. The length g of the lighting fitting varies with the length of the sources of light employed; in the present case this length is about 1 metre.

With the embodiment of the lighting fitting shown in Fig. 2 it is not strictly necessary that the lenses should engage one another at their edges. If desired, smooth straight, transparent or non-transparent parts may be provided between these lenses. In the embodiment shown the lenses are shown as being lano-convex lenses; however, they may be double convex or, if desired, be constituted by socalled fresnel lenses.

What is claimed is:

1. A street lighting fixture comprising a frame, a source of light constituted of a plurality of substantially cylindrical discharge tubes, means mounting said tubes in a vertically superposed manner in said frame, and a plurality of elongated convex lenses each being spaced from and parallel to each of said corresponding tubes and having a substantially horizontal focal line and optical bottom point of said tube and passing through the optical 5 center of said lens and being at an angle of from 10 to 30 to said optical axis, and the angle constituted by a line extending from the top part of each tube to the optical center of the next higher lens and the line extending from the bottom part of an adjacent superposed 10 discharge tube to said last named optical center is at least 10".

2. A street lighting fixture as set forth in claim 1 wherein the edges of two adjacent lenses engage each other.

aaaaaae 6 References Cited in the file of this patent UNITED STATES PATENTS Margolis Sept. 26, 1950 FOREIGN PATENTS Great Britain Feb. 11, 1953 France May 20, 1953 Germany Sept. 3, 1953 France Nov. 25, 1953 Great Britain Aug. 4, 1954