DIMMING APPARATUS

Abstract: In a mechanical light dimmer system of the type having opposed dimmer plates to be moved laterally into the light beam of a projector the edges of the dimmer plates are connected with shortly projecting diffusor plates, such that these will be fully operative only when the dimmer plates are almost closed. It has been found that it is thus possible to ensure an evenly illuminated light spot also in the maximum dimming range, without generally reducing the lighting capacity of the projector.

Description: Dimming Apparatus The present invention relates to a light projector with a dimmer system, i.e. a system for adjusting the amount of light present in the light emission from the projector. In many circumstances, e.g. in theatre lighting, it is important to ensure that the light intensity of a given light spot on a surface can be varied between a projector determined maximum and zero, and while this could be achievable by an adjustment of the light emission from the projector bulb itself, it is nevertheless preferred to make use of adjustable dimmer plate systems operable to gradually shade off the light transmission from the bulb, particularly because relevant modern discharge bulbs are not suited for full radiation adjustment. Moving dimmer plates into the light beam at a position spaced from the focal point of the projector will not alter the size of the light spot, but only the light intensity thereof. However, in order for the light spot to remain stable and evenly illuminated, it is a condition that the dimming is effected in a symmetrical manner about the middle axis of the light beam, not necessarily in accordance with the iris principle, but preferably from opposite sides of the light beam. This has lead to several different working principles, e.g. opposed "closable doors", opposed displaceable finger plates, or rotary dimmer plates with circularly-arranged wedge-shaped slots. In connection with the invention it has been observed that as the dimming proceeds towards a low light intensity in the light spot there appears a certain, visible distortion of the light, giving rise to unevenness of the light distribution in the light spot. It is believed that this is due to extremely small inaccuracies in the sharpness of the edges of the dimmer plates or perhaps to previoμsly described circumstances around light passage over sharp corners or, respectively, to irregularities in the light source itself or other optical inaccuracies. According to the invention this problem is overcome by the provision of light diffusor means arranged in direct or indirect association with the edges of the dimmer plate system, extending somewhat beyond the relevant light cutting edges thereof so as to cause the light distribution just next to these edges to be diffused at least in the lower adjustment range of the light intensity. It seems that the said problem does not occur if the light, generally, is emitted through a diffusor filter, but any such filter will inevitably cause some reduction of the maximum brightness of the light spot and is, therefore, undesirable in practice. A similar, though reduced attenuation, of course, will arise from the introduction of the diffusor plates next to the light cutting edges of the dimmer system, but for good reasons this no longer affects the maximum light intensity, and it has been found that the introduction of the free edge of a diffusor plate into the light beam does not give rise to any noticeable distortion of the light distribution in the light spot. Viewed from one aspect, the invention provides a projector with a mechanical light dimmer system comprising light blocking plate means arranged in a cross movable manner relative to the light beam of the projector so as to exhibit light beam cutting edge portions gradually adjustable between an open position, in which the light beam is fully or widely non-dimmed, an almost closed position, in which the light beam is widely dimmed, and a closed position, in which the light beam is entirely blocked, characterized in that the light dimmer system is provided with diffuser element means which are operable so as to be generally held outside of the light beam as long as this beam is widely non-dimmed, while in the dimming area next to said almost closed position said diffuser element means will be partially intruding into the light beam, while further towards said fully closed position the diffusor element means will be present throughout the entire cross section of the effective light beam. A diffusor element may be mounted so as to cover only the pointed end of a generally V-shaped recess in a light dimmer plate. The light blocking plate means may be mounted so as to be pivotable into the light beam about an axis located crosswise of the light beam. In connection with the associated light beam edge cutting portions there may be rigidly fixed a diffusor element in such a geometrical position that this element, during pivoting of the light blocking plate means into the light beam, is initially shadowed behind said light beam cutting edge portion, while in the course of pivoting into said fully closed position the diffusor element is swung progressively into the light beam for full coverage thereof during the final phase of the pivoting of the light blocking plate portion into its fully closed position. The diffusor element or elements may exhibit substantially the same diffusor effect all over their active area. It would be possible to make use of diffusor plates, e.g. of frosted glass-, prepared so as to be practically non-distorting adjacent their free edges and gradually more distorting towards their transition to the light cutting edge of the dimmer system, but in practice this does not seem to be required for achieving a fully acceptable result. The diffusor plates may be of any usable type, whether with moulded or worked out surface irregularities of a transparent plate or with a printed spot pattern of light shading spots on one or both sides of a transparent plate. Even a spot or surface printing with graduated light penetration characteristics could be considered. In the following the invention is described in more detail with reference to the drawings, in which: Figure 1 is a perspective view illustrating the principle of the invention; Figure 2 is an elevation of an almost closed dimmer unit; Figure 3 is a sectional view of a practical embodiment of the invention; Figure 4 a perspective view of a part of the embodiment of Figure 3 ; Figure 5 as an elevation of a modified traditional dimmer plate; Figure 6 is a perspective view of a development of the embodiment of Figure 3 ; Figure 7 is a reverse perspective view of the embodiment of Figure- 6; Figure 8 is an elevation of the embodiment of Figure 6 ; and Figure 9 is a plan view of the embodiment of Figure 6 in the position of Figure 8. In Figure 1 is shown a reflector lamp 2 forming a light spot 4 on any relevant surface. In front of the lamp 2 there is arranged a pair of dimmer plates 6, each having an inwardly open V-incision 8 and each connected to movement control means 10 operable to displace the plates towards and away from each other, sliding across each other. It is easily understood that the V-incisions 8 can be controlled thus to effect any degree of attenuation of the light beam from the lamp 2, down to a complete shutting off of the beam. The light spot 4 will maintain its diameter, but its light intensity will decrease towards zero as the dimmer plates 6 are displaced inwardly. Figure 2 shows a situation in which there is only a small diamond-shaped hole 12 left between the plates before a complete shutting off (or after an initial opening from a shut-off position) of the plates 6, the relevant light beam being represented by a circle 14. According to the invention, the innermost bottom (deepest) portions of the V-incisions 8 are filled out or covered by a translucent plate member 16 of "frosted" type, i.e. having irregularities resulting in a more or less pronounced diffusion of the light penetrating the translucent plates. In the fully open positions of the dimmer plates as shown in Figure 1 these sub-plates 16 are located entirely outside of the light beam, i.e. they will not give rise to any kind of attenuation of the light intensity of the light spot 4. As the dimmer system is closed (Figure 2) , the frosted plates 16 will gradually fill out an increasingly larger percentage of the diamond hole 12 until this hole is completely closed, and as mentioned this will result in a highly even light distribution in the light spot 4, even in the lowermost range of the adjustment interval, just before final shutting-off or opening-up of the light beam. Figures 3 and 4 show another embodiment, where the entire dimmer system is only as broad as the reflector lamp 2 itself. The system comprises two opposed dimmer plates 18 each arranged so as to pivot about an edge axis 20, whereby they can be swung together from a fully open position as shown in full lines towards a fully closed position in front of the reflector. Adjacent and outside its other free edge, each plate 18 carries a frosted translucent plate member 22 slightly spaced from the plate 18 and slightly projecting beyond the outer edge thereof. During, the initial and major part of their closing movement the dimmer plates will shadow for their own frosted plates 22 until the position PI as shown in dotted lines is reached. After this stage, as illustrated by position P2, the frosted plates 22 will be brought increasingly into the light beam or stripe which is still emitted between the edges of the dimmer plates, and finally the light beam, now in its entirety passing through the frosted plates 22, will be cut off when the dimmer plates are brought fully together, preferably with some overlapping at their outer edges . In connection with such a final overlapping it is preferred to design the dimmer plates with a slightly V-shaped configuration of their free edges, as illustrated in Figure 4. This will ensure that the final attenuation of the light to zero can be controlled in a gradual and well defined manner. Figure 5 shows a well-known type of an adjustable dimmer plate arranged as a rotary plate 26 provided with an arched (arcuate), wedge-shaped recess 28. The plate is placed in front of the light source 2 with the latter located slightly laterally offset from the centre of the plate or disc 26. It is readily understood that the dimming of the light will be adjustable between "fully open" and "fully closed" all according to the angular setting of the wedge recess 28 relative to the lamp 2. In this connection, it is very easy to implement the principle of the invention, viz. just by adding a diffusor element 30 to cover the narrow end of the recess. What will remain, however, is that this solution will still require a wide mounting space at the side of the lamp. Figures 6 to 9 show a further embodiment of the invention which is a development of the embodiment of Figure 3. According to this embodiment, the diffusers 22 are each mounted on a respective spacer member 32 which is attached to the respective shutter 18. The shutters 18 are rotatable about respective pivots 34 under the control of an electric motor 36. The pivots 34 are spaced from the plane of the respective shutter 18. The electric motor 36 drives one of the shutters 18 directly, and the rotational movement is conducted to the other shutter 18 via a transmission member 38 which is pivotally connected at each end to the base of each shutter 18. The diffusers 22 are mounted relative to the shutters 18 such that, as the shutters 18 are rotated about the pivots 34, the diffusers 22 diffuse light at the edges of the light path defined by the gap between the shutters 18. In this way, as shown in Figure 8, when the space between the shutters 18 is relatively small for high attenuation of the beam, the diffusers 22 diffuse substantially all the light passing between the shutters 18 to provide even illumination. The spacing of the diffusers 22 from the shutters 18 in the direction of the light beam (indicated by arrow A in Figure 9) provides a more homogeneous diffusion effect when the light beam is converging towards the space between the shutters. Viewed from a further aspect therefore the invention provides dimming apparatus for a luminaire comprising at least one shutter which is movable, in use, to dim a light beam by restricting the cross- sectional area of the beam and at least one diffuser which is arranged to diffuse light in a perimeter region of the cross-section of the light beam adjacent the shutter, wherein the perimeter region is smaller than the cross-sectional area of the unattenuated light beam, and the diffuser is spaced from the shutter in the direction of the light beam. The diffuser may be arranged for movement with the shutter. In particular, the diffuser may be " connected or mounted to the shutter. The shutter and/or the diffuser may be arranged to rotate about a pivot. The pivot may be common to the shutter and diffuser. The dimming apparatus may comprise a spacer member arranged to maintain the diffuser and shutter in spaced relation. The spacing between the diffuser and the shutter may be greater than 1mm, greater than 2mm, greater than 3mm, greater than 4mm or even greater than 5mm. The invention extends to a luminaire comprising a light source and dimming apparatus according to the invention. The diffuser may be spaced towards the light source relative to the shutter. In summary, in a mechanical light dimmer system of the type having opposed dimmer plates to be moved laterally into the light beam of . a projector the edges of the dimmer plates are connected with shortly projecting diffusor plates, such that these will be fully operative only when the dimmer plates are almost closed. It has been found that it is thus possible to ensure an evenly illuminated light spot also in the maximum dimming range, without generally reducing the lighting capacity of the projector.

Claims: Claims 1. A projector with a mechanical light dimmer system comprising light blocking plate means arranged in a cross movable manner relative to the light beam of the projector so as to exhibit light beam cutting edge portions gradually adjustable between an open position, in which the light beam is fully or widely non-dimmed, an almost closed position, in which the light beam is widely dimmed, and a closed position, in which the light beam is entirely blocked, characterized in that the light dimmer system is provided with diffuser element means which are operable so as to be generally held outside of the light beam as long as this beam is widely non-dimmed, while in the dimming area next to said almost closed position said diffuser element means will be partially intruding into the light beam, while further towards said fully closed position the diffusor element means will be present throughout the entire cross section of the effective light beam. 2. A projector according to claim 1, in which a diffusor element is mounted so as to cover only the pointed end of a generally V-shaped recess in a light dimmer plate. 3. A projector according to claim 1, in which the light blocking plate means are mounted so as to be pivotable into the light beam about an axis located crosswise of the light beam, whereas in connection with the associated light beam edge cutting portions there is rigidly fixed a diffusor element in such a geometrical position that this element, during pivoting of the light blocking plate means into the light beam, is initially shadowed behind said light beam cutting edge portion, while in the course of pivoting into said fully closed position the diffusor element is swung progressively into the light beam for full coverage thereof during the final phase of the pivoting of the light blocking plate portion into its fully closed position. 4. A projector according to claim 1, in which the diffusor element or elements exhibit substantially the same diffusor effect all over their active area. 5. Dimming apparatus for a luminaire comprising at least one shutter which is movable, in use, to dim a light beam by restricting the cross-sectional area of the beam and at least one diffuser which is arranged to diffuse light in a perimeter region of the cross-section of the light beam adjacent the shutter, wherein the perimeter region is smaller than the cross-sectional area of the unattenuated light beam, and the diffuser is spaced from the shutter in the direction of the light beam. 6. Dimming apparatus as claimed in claim 5, wherein the diffuser is mounted to the shutter. 7. Dimming apparatus as claimed in claim 6, further comprising a spacer member arranged to maintain the diffuser and shutter in spaced relation.

Inventors: SCHMIDT FINN, SCHMIDT, FINN
Applicants: MARTIN PROFESSIONAL AS, SCHMIDT FINN, MARTIN PROFESSIONAL A/S, SCHMIDT, FINN
Application year: 2001
Main classification: F21S8
IPC codes: F21S8, F21V11, F21V13