Illumination – Light source and modifier – Adjustable or repositionable modifier
Patent
1999-02-05
2000-08-15
Cariaso, Alan
Illumination
Light source and modifier
Adjustable or repositionable modifier
362283, 362293, 362321, 362323, 359889, F21V 1408
Patent
active
061025542
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for modifying a light beam, in particular in apparatus comprising a light source and means for directing and/or focusing the light.
Embodiments of the invention relate to a colour changer, to a diaphragm and to a light dimmer. More particularly, the invention relates to an arrangement of moveable blades (a) in a colour changer for changing the colour of light in a light beam, (b) in a diaphragm for varying the aperture, and (c) for dimming a light beam.
It is desirable, in many lighting applications, to be able to vary the colour of light projected, for example spot lighting at discos or rock concerts or other varied, coloured lighting.
A colour changer is known from U.S. Pat. No. 4,893,225, and comprises a plurality of coloured, translucent leaves rotatably attached to a support frame and means for moving the leaves between a closed position and an open position to vary the colour of a light beam passing through intercepting leaves.
However, the total width of the mechanism is large, being approximately two and a half times the maximum width of the beam of emitted light. For lighting applications requiring large beams the width of this colour changer is prohibitive.
It is also known to scroll coloured plastic film across a light beam. The film is conveniently stored but rapid changes of colour are generally not possible.
Conventional iris-type diaphragms, found for example in cameras, projectors and spot lights, typically comprise a plurality of overlapping blades, the blades being moveable to vary the diaphragm aperture. In a known arrangement, described in EP-A-0372932, a set of overlapping blades are disposed around a central aperture. Each blade is mounted on one fixed pivot and one moveable pivot wherein movement of a cam against the moveable pivot rotates each blade so as to vary the diaphragm aperture.
Blades of such conventional diaphragms slidingly and touchingly overlap each other. It is accordingly necessary for blades to be thin and smooth and to be adapted to slide over each other, which may require some form of lubrication. When thin blades are used for long periods with a high intensity light source the blades can become very hot; excess heat can distort blade shape and may impair the function of the diaphragm.
In operation of known diaphragms, blades positioned for maximum aperture lie substantially flat and in the plane of the diaphragm, normal to the direction of light passing through the diaphragm. As the blades rotate towards the centre of the diaphragm, reducing the aperture, blades overlap with successively more other blades. The effect of the overlapping is that a portion of each blade is twisted up and out of the plane of the diaphragm. Consequently, blades can only be made out of a resilient, flexible material--which may not have ideal heat resistant properties.
Another disadvantage of this arrangement is that the diaphragm can not be completely closed, but instead has a minimum aperture, illustrated for example in FIG. 2 of EP-A-0372932. To close substantially completely the aperture, an additional shutter is required. This additional shutter can be bulky and if it can not be retracted out of the light beam, when not in use, can interfere with the light beam.
Instead of operating an additional shutter to close the aperture, the light source, such as a bulb, can be extinguished. This presents a problem in that frequent lighting and extinguishing of the bulb decreases its lifetime.
It is also known to dim the output of lighting apparatus. Incandescent bulbs can be dimmed to a certain extent by varying the power supplied, but this dimming can change the light colour temperature. Discharge lamps can not generally be dimmed in this way. When projecting stage or concert lighting it is known to provide at the outside of a spotlight a shutter arrangement to dim the emitted light. One such arrangement is an Aldis shutter made up of a series of rotatable, louvred blades. These rotate along an axis normal to the direction of light, thus when open they rem
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Morrell David
Wynne Willson Peter David
Cariaso Alan
Wynne Willson Gottelier Limited
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