IE910979A1 - Display lighting - Google Patents

Description

LgU i iD'i * ___ r&T10H TRUE COPY ___,,, 1 . - ' *? 1 \ I /·> - Λ- } r·.' Γ; " · ; ^ \ t O Li Ό ** J | *1 „lCM\o«w...............p'isPi- SPECff'C^'0, of Dunsland, ®resi • sh citizen* ° nmWOR^* an ln · n-f Ireland. «» -tr:-Re?ubi,c Mount Mention, 060AS ft ids ./ ® . ffL ‘ The present invention relates to display lighting, in particular to a spotlight or floodlight which may be adjusted to project a uniform focussed beam of light extending only as far as thfe extremities of the display object. ^ For display lighting, or to produce special.lighting effects, a spotlight producing a strong, generally circular beam of light may be used. Conventional spotlighting casts a strong beam of light over a limited area, but generally cannot be focussed on an object, i.e. the further the object is from the spotlight, the more disfuse the light. Also, the beam cannot easily be adjusted to fall only on the display object, and stray light passing the object casts a strong shadow. The same applies to conventional floodlighting.

Spotlights used for stage lighting are more powerful and normally include a lens to focus the beam into a well-defined circular or elliptical pool of light, which may be varied in size by the use of a diaphragm shutter arrangement, which varies the diameter of an aperture between the bulb and the lens.

However, a dramatic effect can be achieved when a uniform focussed beam of light is projected onto the display object, without passing the object, so that no shadow is cast. This effect may be demonstrated 2 S?® i $ {< / g o with a conventional slide projector in limited circumstances. For example, when a slide projector is set up to project a horizontal beam of white light onto a vertical wall or screen (i.e. with no slide in the slide carrier), an enlarged image of the slide carrier opening will be projected on the wall, which should be rectangular in shape, and which may be focussed with the lens to give a crisp edge all round. If a picture of corresponding rectangular dimensions is hanging on the wall, the beam may be precisely focussed so as not to stray outside the extremities of the picture frame, which produces a very dramatic display effect. Because of the condenser lenses employed in the slide projector, a reasonably uniform field of light is produced.

However, the conventional slide projector is incapable of producing this desirable effect when deployed at an angle to the horizontal, because the projected beam will tend to appear on the wall as a trapezium, i.e. with only a pair of sides parallel, or as a trapezoid, i.e. with no sides parallel. Quite apart from this drawback, a slide projector system would be unsuitable for display lighting purposes as it is cumbersome and a coaling fan mechanism is also required to keep the bulb cool.

The present invention overcomes these difficulties by providing a compact spotlight arrangement which may be adjusted to project a beam of light of any desired dimensions onto a display surface or display object, which does not depend upon the angle of projection, e.g. the attitude or angle at which the spotlight is mounted on a wall or ceiling. For example, the invention provides an overhead spotlight system, which may be used in a picture gallery, wherein individual pictures are illuminated by separate spots, each having its beam adjusted and focussed so as to fall within the exact dimensions of the various picture frames. The invention generally provides a spotlighting system where the dimensions of the incident beam may be pre-determined and where the incident angle or the angle of projection is compensated for precisely by adjusting the dimensions of the projected beam. For instance, an incident beam appearing on a display surface as a quadrilateral is actually projected at an angle to the surface as a trapezial or trapezoidal beam, such that the shape of the projected beam may be varied by means of a variable shutter 3 It· 10*/.«· arrangement, to produce the’required incident beam. However, the invention also provides a system whereby static display objects with irregular outlines, even three-dimensional objects such as pieces of sculpture, may be illuminated wherein the beam is permanently adjusted to match the outline of the display object, and focussed so as not to cast any stray light past the object's outline.

According to the present invention there is provided a display lighting system contained within a housing including a light source, aperture means to restrict the extent of a beam of light produced by the light source, and light beam focussing means, wherein the aperture means is disposed between the light source and the focussing means, characterized in that the aperture means is adapted to be adjustable firstly to produce an incident beam exactly coincident with the outline of an object within its field of focus, and secondly to compensate exactly for the azimuth and elevation of the incident beam whilst remaining coincident with the outline of the object. Λ The light source is preferably a spotlight'including a reflecting mirror. The spotlight is preferably a reduced voltage lamp such as a quartz halogen lamp, and the mirror is preferably dichroic.

The aperture means preferably comprises a plurality of independently movable light-opaque shutters, each mounted in, and movable relative to, the housing, and each adjacent pair of shutters being mounted for overlapping movement so as to define between them a variable aperture.

Preferably the shutters are mounted in slits in the housing so as to project outside the housing for external manipulation.

The shutters are preferably adapted for stiff sliding movement relative to the slits. There are suitably four shutters, each including an outwardly-biased flap portion providing said stiff sliding movement relative to the slit.

Most preferably, the shutters may be arranged to define a quadrilateral aperture therebetween. 4 ί.-Ι10δ?β$ ",Ί The light beam focussing means preferably comprises a pair of lenses spaced apart to give a nett focal length of about 50 - 75mm. Alternatively a single lens of a focal length of about 100mm may be provided. Most preferably the arrangement is such that the lens "f number" (ratio of focal length to lens diameter) is a number greater than 2, so as to limit the effect of spherical aberration.

In another aspect, the present invention provides a method of illuminating a static display object having an irregular outline with the system described above, comprising the steps of - temporarily removing the aperture means, and fixedly mounting the lighting system to a mounting surface, - illuminating the object with a light source, and optionally masking the object with a monochromatic material, - placing a monochromatic photographic plate or the like within the field of focus of the focussing means and exposing the plate, - removing the plate and developing a positive transparency of the object, - replacing the aperture means by the said transparency, - projecting a beam of light through the transparency to fall on the object and positionally adjusting the transparency if necessary so that the incident beam is exactly coincident with the outline of the object.

The photographic plate may alternatively comprise opaque material with an etch-resistant coating enabling an outline corresponding to the object to be etched from the developed plate.

The invention will now be described in further detail with reference to the accompanying drawings, in which 5 tS10S7#i Μ Figure 1 is a side elevation in longitudinal cross section of a ceiling - mounted spotlight in accordance with a first embodiment of the invention, with shutters removed for clarity, Figure 2 is a sectional view of the spotlight of Figure 1 viewed on Section A-A, showing the shutters in place, Figure 3 is a side elevation of one of the shutters during manufacture, before being bent, Figure 4 is a side elevation of a finished shutter, Figure 5 is an end elevation of the shutter shown in Figure 4, Figures 6a to 6d illustrate the shape of an incident beam of light projected through a square aperture onto a vertical surface from various different positions, for example using a conventional slide projector, and Λ Figure 7 illustrates the projection of, for example, square incident beams onto a vertical surface from above at various different positions using a display lighting system according to the present invention.

Referring firstly to Figure 1, a spotlight 1 comprises a cylindrical metal housing 2, having an end cap member 3 at one end adapted to hold a lamp 4 in place between an end rim 5 of the cylinder 2 and a spring 6. The end cap 3 fits over the cylinder 2 and is held in place by a bayonnet fitting 7 which is in turn held firm by the spring 6 which tends to urge the end cap 3 away from the cylinder 2.

The lamp is preferably a dichroic quartz halogen lamp, for example a Thorn - EMI "Micro Graphic" spotlight lamp of, for example, 50mm diameter, 50 to 85 Watts, and operating at a voltage of 13.8 V. A lamp of this type has the following advantages; (a) It has a spherical reflecting mirror behind the bulb, (b) The mirror is dichroic, that is, infra red energy falling on the mirror is absorbed by it and re-radiated from the back of the 6 fe§'&87§H mirror, resulting in a cooler beam of visible light which is less likely to damage delicately coloured material, (c) It is of low voltage producing a high lumen/watts efficiency, (d) It produces a converging beam, that is, an image of the lamp filament is produced a short distance in front of the bulb ,and (e) It is available in a variety of sizes and wattages.

The other end of the cylindrical housing 2 is adapted to contain a lens or lens assembly. In the illustrated embodiment, two biconcave lenses 8 are held inside a plastics barrel 9 which is externally screw - threaded to engage a indent or protuberance 10 on the inside of the cylinder 2. A flange 11 at the front of the barrel 9 is preferably adapted to retain an ultraviolet filter (not shown). Thus, by turning the barrel with respect ot the cylinder, the lens assembly may be moved axially with respect to the lamp to provide a means of focussing a beam of light produced by the lamp. λ A shutter arrangement is located between th6 lamp 4 and the lenses 8. The purpose of the shutters is to restrict the beam of light produced by the lamp to pass through an aperture defined by a gap between the shutters. In the illustrated embodiment, four shutters 12 are slid into respective slots 13 formed in the cylinder 2, one from above, one from below, and one from each side, so as to overlap, as seen in Figure 2. The shutters 12 are preferably made of thin metal plate of the shape shown in Figure 3, and bent into the shape shown in Figures 4 and 5 to produce a plate portion 14 and a springing tongue portion 15. The shutters are of an opaque material, such as steel with a phosphoric matt black surface finish. A small hole 16 may be provided to facilitate dipping during the finishing process. It will be apparent from Figure 2 that the individual shutters may be moved in and out in their slots and levered from side to side against the friction of their tongue portions 15 to produce a gap 17 therebetween of generally quadrilateral outline. By virtue of the curvature of the cylinder 2, the shutters 12 tend to remain perpendicular to the axis of the cylinder. The springing action of the the tongue of each shutter ensures frictional resistance to movement so that once adjusted it remains so. 7 * fi 1 Ο 9 7 β ·; Small triangular areas 17a formed between adjacent shutters 12 adjacent the cylinder 2 may allow light to pass through, but generally these will not be focussed and projected by the lens. However, if these become visible and are objectionable they may be masked by a suitable collar or diaphragm for example.

The shutters are at a distance away from the lens approximately equal to the focal length of the lens - in the illustrated arrangement, it is the nett focal length of both lenses. For instance a single lens of focal length 100mm may be used or two spaced lenses of nett focal length 50 - 75mm may be used. Thus a beam of light of a variable quadrilateral section is projected through and focussed by the lenses to fall on a surface as an incident beam, the shape of which will be an inverted image of the aperture formed by the gap 17, provided of course that the spotlight is in a horizontal plane perpendicular to a vertical surface onto which the beam is projected. The "f number", i.e., the ratio of the lens focal length to the lens diametef', is preferably greater than 2 for this application, to avoid any visible effects of spherical aberration. This would be apparent as a bowing or bending of the otherwise straight edges of the incident beam. Chromatic aberration causes little undesirable effect in this application, but may if necessary be corrected in a manner known, per se.

If the lamp were to be located too near the shutters, it would also be near the focus of the lens. The bulb filament would appear a very bright spot surrounded by a halo (an image of the mirror), but by moving the lamp back from the shutters its image becomes more and more out of focus and the projected light becomes more uniform. A position can be selected to give a satisfactory field of illumination without the need for a condenser lens between the lamp and the shutters, which distinguishes the arrangement from a conventional slide projector.

Now if the shutters were to define a square aperture, a square incident beam 19 would be produced on the vertical surface when the light is projected in a horizontal plane perpendicular to the surface, from a point 18 (see Figure 6b). If light is projected from a point 20 above point 18, i.e. with angle of elevation greater than zero, a 8 w ® 1 ο 8 * 9J; trapezia! incident beam 21 Is produced. If light is projected from a point 22 below point 18, i.e. with angle of elevation less than zero, a trapezial incident beam 23 is produced. If light is projected from a point 24 with a different angle of azimuth, i.e. in a plane not perpendicular to the surface, and from above, the incident beam will be a more complex trapezoidal shape 25. As mentioned above, these effects may be produced by a conventional slide projector without a slide in the holder. The arrangement of the shutters 12 in the present invention, may be used to counteract these effects quite simply wherein the shutters are firstly adjusted to the appropriate trapezial or trapezoidal shape which will produce the desired square or rectangular incident beam. This is illustrated in Figure 7, wherein three square incident beams 26, 27, 28, are produced from three different projection points above; the approximate shape 29, 30, 31, of the aperture formed by the shutters is shown schematically in each case.

It is quite a simple matter to manipulate the shutters as one simply observes the varying shape of the incident beam on a surface such as a wall in a darkened or dimly lit room/'until this coincides exactly with the area to be illuminated by the spotlight, which may for example be a picture in a frame, an alcove, a display cabinet, an exhibition display screen, etc. Once the shutters are properly adjusted, they remain locked in position. It is also important that the spotlight remains firmly fixed relative to its mounting surface, which is achieved by a suitable mounting bracket seen in Figure 1.

The mounting bracket 32 comprises a cylindrical member which is bored from two sides to allow electrical cable 33 to pass from a transformer 34 to the lamp 4 through an opening in the end cap 3. The bracket 32 is fitted into an opening in the transformer housing and held firmly in place by a spring steel washer 35 on the inside and a rubber 0 - ring 36 seated on a flange to the outside. In the illustrated embodiment, the transformer 34 forms an integral part of the mounting and must itself be fixed to a wall or ceiling. The bracket 32 must be secured with a tight connection to allow it to turn stiffly, to adjust the azimuth setting. The housing 34 may be used to house the required transformer or alternatively if the transformer is mounted remotely, the housing 34 may be reduced in size to a raised 9 L· & \ Oj Q 7/ g oj baseplate containing only electrical connections. It will be appreciated that one transformer may be employed for several spotlights, for example mounted individually on mounting plates, on a track, in a duct or flush to a ceiling in a recess. A pair of lugs 37 on the cylinder 2 is used to hold the cylinder in firm engagement with the bracket 32. Again this is a tight enough connection to allow the angle of elevation to be adjusted and remain so.

If the object to be illuminated is not a picture, or other relatively flat object or surface, but is a three - dimensional object such as a bust or sculpture, the apparatus may be adapted to produce the same very dramatic lighting effect whereby only the object is illuminated without casting a shadow. This is accomplished by firstly mounting the spotlight in the desired location and fixing it securely so that its light is cast on the bust. The bust is then preferably prepared by covering it in a white masking film, and a black backdrop is also put in place. The shutters are removed temporarily from the apparatus which is then used temporarily as a camera. A strip of photo - sensitive monochromatic material (e.g black and white film) is placed in through the slits 13 under dark room conditions. The whitened bust is then illuminated for a sufficient time to properly expose the photographic material. This is the removed, again under dark room conditions, and developed. After development (in positive) the bust will be a clear transparent area in the centre of the transparency.

The remainder will be dark and opaque. The transparency is then reinserted into the apparatus and the lamp is switched on. The white masking film is removed from the bust. The position of the transparency is finely adjusted so that the image projected coincides exactly with the outline of the bust from the aspect of the spotlight.

When properly executed, no light passes the bust and a most dramatic effect is achieved. This method may be employed to illuminate a circular or oval picture or surface also.

Alternatively, a circular area may be illuminated as follows. A copper disc is coated on both sides with a photo - sensitive and etch -resistant material and is then inserted in the spotlight cylinder so that the disc is at the focal plane. The disc is exposed as before but 10 fci ί097$. preferably under ultraviolet light, using the apparatus as a camera, for an appropriate period, e.g. about half an hour. The disc is then removed, developed, and etched to result in a copper disc with an elliptical hole which is reinserted in the cylinder at the focal plane to act as a shutter. From the aspect of the spotlight, light projected through the ellipse will fall on the incident surface as a circle, compensating for the angles of elevation and azimuth of the spotlight mounting, as described above.

When deployed in a picture gallery or an an exhibition display, the system may include a single on/off switch linked to a passive infra red detector or the like so as to switch on automatically when a person enters the viewing area.

In the illumination of really valuable paintings it is of the utmost importance that the incident light should not damage the painting. Ultraviolet light causes degradation of the pigments in paintings, fabrics and materials, films and varnishes may protect paintings for a limited time, but these too yellow and degrade and must be replaced. An ultraviolet filter may be placed in front of the lens as mentioned above, on a disc-shaped filter may be placed directly in front of the lamp, such as an OPTIVEX (trademark) filter by Bausch and Lomb.

Dated this 25th day of March 1991.

By: TOMKINS & CO., Applicant's Agents, (Signed): 5, Dartmouth Road, DUBLIN 6. 11