US 3139604 A
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June 30, 1964 Q O m g ETAL 3,139,604
LAMPS AND LIGHTING EQUIPMENT Filed Feb. 29, 1960 In Deniers.
, ttorneys a A 3,13%,6M Ce Patented June 30, 1964 3,139,604 LAMPS AND LIGHTING EQUIPMENT Carl Otto Meiners, fitnttgart, Germany, and Heinz Walter Lessing and Walter Benito Lessing, both of London,
England, assignors to Meiners Optical Devices Limited,
London, England, a British company Filed Feb. 29, 1969, Ser. No. 11,744 Claims priority, application Great Britain Mar. 3, 1959 2 Claims. (Cl. 340--25) This invention is concerned with lamps and lighting equipment. I
In recent years greater traffic density and higher speeds have led to increasing attention being paid to lighting problems, both for surface and air traffic. Great progress has been made in the technique of lighting at night, but this has not been matched where penetration of haze and fog is concerned.
Safety considerations make the problem of poor visibility particularly acute where aircraft landing operations are involved. Existing airport lighting systems have guiding lights which embody lamps of great candle-power, in some cases vacuum flash-tubes, together with reflectors to give a directional beam in the manner of a Searchlight. However, this is inadequate in misty or foggy conditions because the most intense beam produced in this manner is dispersed comparatively soon by the particles or droplets in the atmosphere and its abilityto penetrate lost.
Owing to the widespread diffusion of the light, no useful result is achieved even if the energy of the light source of such a lamp is increased in an endeavor to offset the loss of light due to reflection, refraction and absorption in the fog. The only outcome is that the wall or curtain of fog between the lamp and the aircraft is more highly illuminated and the best that can be done with such lamps is to make a very large area of fog visible to the approaching pilot. The runway, which is relatively narrow, is not made visible or demarcated and the pilot is given no help at all in his approach to it. The same kind of problem also occurs in the case of land traffic and at sea.
Therefore, a new approach to the problem is needed.
We have discovered that in producing a lamp to give a penetrating light beam there are considerations the im portance of which has not previously been recognised. One of these is that, no matterhow powerful the light source, the angle covered by the light beam projected from it, that is to say the extent to which the beam diverges, should be kept so small as to be negligible.
A second consideration is that the means of projection of the light beam shall not be such as will lead to any significant scattering of light around the source. Because of this reflectors such asare commonly used are not desirable. I
Our discovery of the great importance of these two considerations points to use of a lamp in which the light is projected in a narrow beam that is parallel-sided, or almost parallel-sided, by means of a lens-projection system. But a narrow substantially non-diverging beam of this character has too small a cross-section-tobe of real practical use. Thus, to take as an example guiding lights for aircraft landing the usual angle of visibility required for these is 14, i.e. a divergence of about 8.
According to the present invention, there is furnished a lamp to provide an outdoor light for demarcation, guiding, signalling and like purposes, which lamp comprises a light-source and a lens-projection system for projecting a beam of light that is substantially parallel-sided or does not diverge more than a few degrees and is substantially free from stray light outside the beam, together with a power drive for continually moving the beam angularly with a to and fro or orbital motion so that a beam of considerable apparent divergence and great visual range is obtained. I
The ratio of the focal length of the lens of the size of the light source should preferably be as high as to 1 or 200 to 1, although beneficial results can be obtained with ratios down to, say 50 or 60 to 1. By the size of the light source is meant the actual distance across the element or source of the lamp from which the light is emitted; i.e. in the case of a filament lamp or an arc lamp the width or length of the filament or are.
To obtain the desired projected beam the light source must be disposed at a distance from the lens substantially equal to the focal length, which means that unless the light source is very small this distance, and hence the length of the lamp, may be undesirably large. To meet this possible difficulty an optical stop can be used next to the light source and having an aperture of any desired size smaller than the source itself. The aperture of the optical stop then becomes the effective light source and the size of the effective source is the diameter of the aperture, while the relevant distance for focus purposes now becomes the distance between the lens and the stop.
It will be appreciated that this conception of stopping down the light in order to preserve a particular dimensional relationship and thereby achieve better beam persistence and penetration is entirely contrary to previous thought on the problem according to which a large light source is considered an advantage.
As to the permissible amount of spread of the beam, an angle of divergence of the order of 3 may be tolerable in certain cases but in general less divergence is preferable, say not more than It may be worthwhile indeed to place the light source in relation to the lens so that it is at a slightly greater distance, e.g. a few millimetres greater, than the focal length, whereby the lamp projects a beam that is, for some distance near the lamp,
a slightly convergent beam.
The movement of the beam may be of a rotational or orbital character, or it may be simply a lateral movement from side to side through a predetermined angle, the latter being generally more useful for ground level applications. A speed of rotation or translation of the beam is A preferably chosen so as to give an appearance to the human eye of a slight flickering of the light which is considered to be more effective than a continuous or a flashing light effect.
Various practical arrangements for carrying the invention into effect will now be described by way of example, with reference to the accompanying diagrammatic drawings in which:
FIGURE 1 is a plan of one embodiment of the inven- ;tion, and
one end and the lens at the other. No scattered or stray light is to be'allowed out of the housing. In mist'or fog particularly such stray light illuminates the particles in the surrounding atmosphere and detracts from the relative brightness of the lamp itself. Without any such scatter producing a surrounding halo of illumination, the strictly localized brightness of the light source itself stands out more clearly againstthe background.
The beam can be moved in the required manner by mounting the housing or trunk of the lamp for oscillating -or-rotary movement on a frame and providing a reciprocating or rotary drive to effect continual bodily movement of the lamp trunk. Or the optical system for projecting the beam can be housed in a trunk that does not contain the light source but is,mounted to oscillate or rotate upon a stationary housing in which the light source is disposed.
Usually, however it will be found most convenient to keep the bulk of the lamp stationary and simply rotate or oscillate an optical element, such as a lens, reflecting mirror .or prism, or optical stop, associated with the beam projection system. The moving optical element can be an element of the system that is necessary tothe projection of a narrow substantially non-diverging beam, or it can be an additional element introduced solely for the purpose of moving the beam.
In FIGURE 1, an arrangement is shown in which a light source 11 situated at one end of a lamp trunk or housing 12 directs light through the aperture of an optical stop 13 to a convex lens 14 producing a substantially parallel beam 15. The beam 15 is reflected out through a window 16 in the side of the trunk 12 by an obliquely set plane mirror 17. The mirror is oscillated angularly about a vertical axis 18 by means of a cam and follower bar 26, the cam being rotated continuously on a vertical shaft 21 by an electric motor (not shown). The motor and appropriate gearing as well as any other electrical components required can be housed in a case on the underside of the lamp trunk.
This kind of apparatus causes the narrow beam 15 to move angularly to and fro to trace out a wedge-shaped light volume. It is also possible, for example by rotating a prism in the beam, to cause the beam to follow an orbital path and producea cone of light.
The beam can be made to perform, if desired, a series of orbits each one slightly displaced from the one preceding it, the beam returning at completion of the series to the initial position and the cycle of orbital movements recommencing. -substantially zero cone angle can be caused to cover a substantial cone angle.
In this way a parallel-sided beam itself of FIGURE 2 shows an arrangement in which the required movement of the beam is effected by rotation of a prism assembly 22 interposed between the light source 11 and :the lens 14. The prism housing 23 is mounted for rotation about a vertical axis by motor-driven gearing 24, the motor being housed in a case 25 under the lamp trunk as before.
In FIGURE 3, beam movement is accomplished by employing a cam-and-follower mechanism 26 to reciprocate the light source 11 vertically in a slide 27, while in FIG- URE 4 the optical stop 23 is reciprocated.
In FIGURE the light from the light source 11 passes through a centralaperture in a concave mirror or reflec- -tor 27 and strikes a small mirror 28. It then is reflected back to the reflector 27 which in turn reflects the light to the lens 14. The small mirror 28 is carried by a magnet 29 that is mounted for angular movement on a'ball-joi'nt at 30, and when the lamp is operating a cyclical energising electric current supplied to energising windings 31 external to the lamp trunk 12 causes the magnet and mirror to oscillate rapidly.
Lamps according tothe invention having applications :both where the beam of the lamp is to serve as a guiding signalor demarcating light when viewed from a distance and where the beam is for use in enabling objects illuminated thereby to be seen. Examples of the former are airthe projection lens used the greater is the power of the projected beam. It is possible to signal information with such a lamp, and for this purpose it is an advantage to be able to vary the speed of the beam-moving drive so as to change the appearance of. the light to a distant observer from a flashing effect to a-continuous light.
In cases where it is desirable to have two or more beams with their origins in proximity to one another, these can be obtained from a single light source. Thus, by placing a light source mid-way along a lamp housing and having lenses or lens systems at opposite ends a beam can be directed out at each end of the housing. The lamp is therefore well-suited to lighting applications calling for a number of different light beams, either parallel or angularly displaced with respect to one another.
Arrangements are also possible wherein, by the combination of two or more lamp beams, a zone of light is produced in which the nature of the light changes more or less abruptly across the zone according to a prearranged pattern.
For instance, such an arrangement can be employed to set up at some predetermined place in space a target of light consisting of a centre spot or area of relatively intense light surrounded by one or more rings of less intense light.
This technique can be especially useful in its application to the guiding of ships and aircraft. Thus an aircraft pilot flying into a target of light of the kind described will know whether he is at the target centre or off it from the intensity or colour of the light observed and can accordingly take guidance as to the course he should set, for example to land on an airport runway. Likewise, a ship entering a harbour can adjust her course according to the intensity of light received from harbour guiding lights.
Onepractical way of setting up such a zone of changing light is by employing two or more intersecting or substantially coincident beams of different spread, the spread of at least the beam of greater spread being achieved by beam movement as hereinbefore described. If two beams have initially the same intensity but are spread by differing amounts and are arranged so that their axes are substantially coincident or intersect at a great distance from the lamp or lamps giving rise to them, the less divergent beam provides a centre area of high intensity light reinforced by the light from the second beam, while the second or more divergent beam provides a zone of light of lower intensity around the high intensity area. The more divergent beam could, in addition, he of lower initial intensity if desired.
Another way of achieving this result is by employing two beams of the same spread but different intensities and causing one to perform a rapid orbital motion around the other.
If a zone of light having bands of different intensity is required rather than a target, as is usually the casein ship navigation applications, the spread of the beam with the greater spread need be in one plane only, or if two beams of the same spread are employed one can be traversed laterally to-and-fro to provide a band of different intensity upon either side of a central band afforded by the other beam.
Similar techniques can be employed with light beams of different colours.
1. A lamp to provide an outdoor light for demarcation, guiding, signalling and like purposes, said lamp comprising a cooperative assembly of a light-source and a lens projection system for projecting a beam of light which is substantially parallel-sided in that it has no divergence greater than three degrees and is substantially free from stray light outside the beam, said lens-projection system being reflectorless in the sense that it includes no reflector element which actually takes part in the production of the beam as distinct from merely changing the direction of thebeam as a whole, theprojection system including an optical stop interposed between the actual light-source and other optical elements of the projection system whereby the aperture of the optical stop becomes the apparent light-source, and the projection system further including lens means of focal length not less than fifty times greater 5 than the dimension across the aperture of the optical stop, and a power drive for rapidly and cyclically moving at least one element of said assembly thereby shifting the beam angularly with a rapidly-repeated pattern of motion such that a substantially unidirectional beam of greater apparent divergence and great visual range is created.
2. A lamp according to claim 1, wherein the ratio of the focal length to the dimension across the optical stop aperture is not less than 100 to 1.
References Cited in the file of this patent UNITED STATES PATENTS Hunter Nov. 10, 1896 Hunter Apr. 13, 1897 Walsch July 5, 1949 Heehler Aug. 19, 1952 Hooker et a1. Feb. 2, 1954 Roth Sept. 27, 1955 Free Oct. 16, 1956 McRea Nov. 19, 1957 Arnold Mar. 8, 1960