LIGHTING FIXTURE

Abstract: The present invention concerns a lighting fixture (1) comprising a main casing (2, 3) adapted to house a light source and at least one lens, and a support member (10, 11) for carrying the main casing in such a manner that the entire main casing can be rotated through 360 DEG about its optical axis.

Description: LIGHTING FIXTURE The present invention concerns high intensity light fixtures generally known as lummaires. Luminaires can be used both for theatre, studio and architectural lighting applications. One problem with luminaires which is particularly applicable to theatre and studio applications is that there is often a requirement for the lummaire to provide patterned illumination. In order to achieve th s many luminaires are provided with what are known as shutters. These are metal plates which can be moved into and out of the optical path of the lummaire so as to partially obstruct the light beam. Often a lum aire will be provided with at least four shutters though of course the complexity of the pattern which can be generated can be increased by increasing the number of shutters. However increasing the number of gates increases the weight, complexity and cost of a lummaire. As a result of the above problem it has been proposed to provide the front portion of a lummaire, that is that part which is located after the actual light source and which contains the focusing lenses, as a partially rotatable barrel. However such rotatable barrels have had a limited degree of rotation and thus provide only a limited improvement to the range of patterns which can be provided by the lummaire . There are also additional problems with regard to rotatable barrels brought on by the fact that high intensity luminaires generate a considerable amount of heat which in turn causes expansion and ensures that providing a rotatable barrel which is both accurate in use and easy to use is a difficult problem. The present invention is concerned with providing a solution to the above problems. In order that the present invention may be more readily understood an embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side view of an embodiment of a lummaire according to the present invention; Figure 2 is a view of the light-emittmg end of the lummaire of Figure 1 ; Figure 3 s a perspective view of the casing which rotatably mounts the lummaire of Figures 1 and 2; Figure 4 is a perspective view showing a bearing mounted in the lummaire body of Figure 3; Figure 5 is a perspective view of one type of lens which can be incorporated n the lummaire of Figure 1; and Figure 6 is a perspective view of a second type of lens. Referring now to Figure 1 of the drawings this shows a luminaire 1 having a mam body comprising a rear end section 2 housing a high intensity light bulb and an associated substantially ellipsoidal reflector so as to generate a substantially parallel beam of light; and a front end section 3 which contains a section indicated at 4 for mounting four movable metal shutters 5. The shutters 5 are arranged at 90° to one another and are standard in design. Each shutter has a handle 6 by means of which it can be moved into and out of the optical path of light emanating from the light bulb. The front end 3 includes a section 7 m which the focusing lenses of the lummaire are mounted. A knurled knob 8 associated with a slot 9 enables the lenses to be moved axially along the optical path in the lummaire. Once again the lens system mounted within the front portion is, in this embodiment, totally conventional. In normal operation in a theatrical studio environment the luminaire just described would be supported from a mounting such as the telescopic member of a monopole by being connected to the mounting via a suitable arrangement such as a spigot on the casing of the luminaire which engages a suitable reception member carried on the mounting. However in the embodiment being described the luminaire is provided with a substantially circular rotator casing 10 mounted to the lower arms 11 of an inverted U-shaped member 12. The crosspiece of the member 12 can carry a spigot corresponding to the spigot which would normally be mounted on the actual casing of the luminaire or can be mounted in any other suitable manner. As can be seen in Figure 3 the rotator casing 10 is made from two moulded halves 14 which in operation are bolted together. Each half carries a pair of plastic bearings 15. The bearings 15 are mounted on the rotator casing 10 so they are angularly spaced at 90° around the casing and are arranged to run either in parallel grooves provided in the rear section 2 of the main casing of the luminaire. Because of the presence of the casing 10 these grooves can not be seen but similar grooves 16 are provided in the front end section 3. Thus the luminaire can be mounted via either set of grooves. Each bearing 15 has a central hole through which it is bolted onto a seat 17 m the interior wall of the rotator casing 10 by a bolt 18 and each side of the bearing is provided with a pair of upstanding flanges 19 which engage m respective ones of the parallel grooves 16 the lummaire casing. The bearings 15 are made from any suitable tough and resilient material which is resistant to heat. A suitable material is sold under the trademark Ultem 1010R. When the lum naire is in use it will, as already mentioned, get hot because of the heat generated by its high intensity bulb. The purpose of the bearings 15 is to enable the mounting of the luminaire casing within the rotator casing to be such that if the lummaire casing expands the resilience of the bearings 15 will be able to accommodate the expansion and still allow the lummaire to be freely rotated relative to the rotator casing 10. The arrangement of rotator casing 10, bearings 15 and grooves the lummaire casing enable the entire lummaire to be rotated through 360°. In order to hold the luminaire in place once it has been rotated a desired amount the rotator casing 10 is provided with a lock knob 20 having a screw-threaded shaft 21 which by being screwed into a hole 22 in the rotator casing engages one of the bearings so as to press the bearing into contact with the luminaire casing thus locking the rotator casing and the luminaire casing against relative angular movement. The fact that the bearings are mounted by a single central bolt enables the bearing to flex into contact with the luminaire casing to provide the necessary locking action. As already mentioned the front end section of the luminaire carries a number of lenses for providing final focusing of the luminaire beam. Normally these lenses are spheric or aspheric glass lenses. Unless manufactured to very high tolerances such lenses are liable to a number of aberrations such as spherical coma, astigmatism, distortion and field curvature. A variant of the embodiment described uses one or other of two types of lenses which use what is known as gradient index glass. Such glass is manufactured by Light Paths Technologies and is known as GRADIUM (RTM) . The two types of gradient glass are respectively Radial and Axial . In Radial glass the index of refraction of the glass varies from the centre of the glass to its outer edge. This is illustrated m Figures 5A and 5B. Figure 5A illustrates a circular lens 30 and changes in refractive index in the lens 30 are indicated by the series of concentric rings 31 with the refractive index of the glass increasing or decreasing along the radius Z. Figure 5B is a chart showing graphically this change of refractive index with the bars in the chart corresponding to the changes in refractive index. The other type of gradient glass is axial glass and in axial glass the refractive index changes along the axis of the lens . An axial lens is shown in Figures 6A and 6B. As in Figure 5B, Figure 6B is a graphical representation of the change in refractive index but in this case along the lens axis. The variable refractive index glass used in the lens shown in Figures 5A and 6A is normally manufactured by stacking layers of different index glass together in such a manner that there are no air gaps between the various layers. Layer diffusion can be used to weld the glass layer together. An advantage of gradient lens is that the change of refractive index through the lens has the effect of counteracting aberrations such as spherical, coma, astiguation, distortion and field curvature. It will of course be appreciated that the lens themselves need not be circular as shown in the drawings.

Claims: CLAIMS : 1. A lighting fixture comprising a main casing adapted to house a light source and at least one lens, and a support member for carrying the main casing in such a manner that the entire main casing can be rotated through 360° about its optical axis. 2. A lighting fixture according to claim 1, and including a plurality of bearing members located between the main casing and the support member. 3. A lighting fixture according to claim 2, wherein the bearings are fixed to either the casing or the support member and are made from a resilient material so as to accommodate expansion of the casing caused by heat. 4. A lighting fixture according to claim 3, wherein the support member has a circular surface to which the bearing members are secured, and the casing has a circular track in which the bearing members engage. 5. A lighting fixture according to claim 4, wherein the circular track has two parallel grooves, and each bearing has at least a pair of flanges which engage in respective grooves . 6. A lighting fixture according to claim 5, wherein each bearing comprises a central pad from which the flanges extend, the pad being secured at a central point thereof to the support member so as to be capable of flexing around the central point. 7. A lighting fixture according to any one of claims 5 or 6 , wherein there are four bearing members equally spaced around the circular surface. 8. A lighting fixture according to any preceding claim, and including means for locking the casing against rotation with respect to the support member. 9. A lighting fixture according to claim 7, when dependent on any one of claims 4, 5 or 6, wherein the locking means comprise a screw-threaded member carried by the support member which can be operated to press at least part of a bearing into contact with the casing. 10. A lighting fixture according to any one of the preceding claims, wherein the casing is provided with two tracks, either of which can be engaged in use by the support member. 11. A lighting fixture according to any one of the preceding claims, wherein at least one lens carried by the lighting fixture is a gradient index lens. 12. A lighting fixture according to any one of claims 1 to 10, wherein at least one lens is carried by the lighting fixture, the lens being of glass having a refractive index of 1.7 to 1.9 and a low coefficient of expansion to minimise thermal effect.

Inventors: DEMPSTER RICHARD, FREEBORN MARTIN, STEVEN DAVID PAUL, DEMPSTER, RICHARD, FREEBORN, MARTIN, STEVEN, DAVID, PAUL
Applicants: DEMPSTER RICHARD, FREEBORN MARTIN, STEVEN DAVID PAUL, STRAND LIGHTING LTD, DEMPSTER, RICHARD, FREEBORN, MARTIN, STEVEN, DAVID, PAUL, STRAND LIGHTING LIMITED
Application year: 2000
Main classification: F21S10
IPC codes: F21S8, F21V21