GB2063447A - Lighting Unit with Selectively Positionable Diffuser - Google Patents

Abstract

A studio lighting unit comprises a housing, a light source in the housing, and an optical system for projecting light from the source through an aperture in the housing. A diffuser, Figure 3, for diffusing the light for producing a soft shadow lighting effect is selectively positionable in or out of the light path and presents a planar array of lenticular surface elements, preferably convex aspherical surface portions, to the light transmitted by a Fresnel lens from the source. A manually operable chain drive mechanism is arranged to displace a plurality of co-operating diffuser plates constituting the diffuser, the plates being displaceable on vertically extending pairs of parallel guide rails 23, 24, 25 between a stacked position beneath the lens aperture and a staggered, vertically spread operative position in front of the lens. <IMAGE>

Description

SPECIFICATION Lighting Unit This invention relates to lighting equipment and, to a lighting unit suitable particularly, but not exclusively, for use in film and television studios.

It is generally accepted, that, dependent upon the visual impression required when illuminating a scene set for television relay and/or film recording, two alternative forms of lighting should be available to produce different shadowing effects. One such form is known as the hard edge spot and produces sharp shadows of the illuminated subject for a severe visual effect; the other form is known as soft light and produces a blurred, or diffused shadow for a more restful visual effect.

It is also known to produce both of these lighting forms selectively using a single lighting unit constructed and arranged to be adaptable for such purpose. However, this known unit suffers from certain operational disadvantages which result from its design. In particular; this known unit includes a light source movably disposed within a box-like housing which can be mounted upon an upright stand or suspended from a suitable support as required. The housing carries two optical systems disposed to project light selectively from the source in opposite directions with respect to the housing, to produce the two shadow effects.Adjustment of the unit from one ode to the other requires operation of a mechanism which rotates the entire housing through 1800, rotates a reflector adjacent the source also through 1 800 places the source in the correct position for operation in the selected mode, and which operates a light shuttering arrangement oF, for instance, louvres to avoid light projection rearwardly of the housing in that mode. This mecahnism is cumbersome and sluggish in operation.

According to the invention, therefore, there is provided a lighting unit comprising a housing, a light source disposed within the housing, an optical system for projecting light from the source through an aperture of the housing, a diffuser having a pianar array of lenticular surface elements for diffusing the projected light so as to provide a soft shadow lighting effect, and an arrangement for selectively positioning said diffuser in or out of the path of the light travelling from the source through said aperture.

The diffuser preferably comprises a plurality of plates constrained for vertical movement by a chain drive mechanism from a stacked inoperative position to a light diffusing position in which the plates are parallel and adjacent but unregistered to diffuse the entire output beam. The chain drive may be manually operable. The surface elements are preferably convex aspherical surface portions on the side of the plates which face a Fresnei lens disposed in front of the light source.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a forward perspective view showing the external appearance of a lighting unit according to the invention; Figure 2 is a schematic vertical section through the lighting unit of Figure 1; Figure 3 is a schematic forward perspective view of a chain lift mechanism employed in the lighting unit of Figures 1 and 2, and Figure 4 is a rear perspective view of a diffuser element and its associated end holders, as used in the lighting unit of Figures 1 to 3.

The lighting unit 1 comprises a box-like housing 2 pivotally mounted in a yoke consisting of a pair of upright arms 3 interconnected at their lower ends by a cross-bar 4, this cross-bar being centrally mounted by means of a coupling boss (not visible) on a stem 5 of a support stand. The yoke is readily dismountable from the stand and can alternatively be suspended from an appropriate overhead support is so desired. The front wall 6 of the housing is provided with a large aperture 7, through which light produced by a high power light source 8, such as an electrical incandescent bulb projects for the illumination of scene sets or the like. Detachably connected to the front wall 6 is a closure assembly comprising a frame 9 carrying hinged shutters 10.This arrangement, commonly termed a "barn door" fits over the aperture 7 such that the positions of the shutters 1 0 can be adjusted as required for further control of the lighting effect produced by the unit.

For clarity of illustration the "barn door" assembly is shown detached and axially spaced from the aperture 7 in Figure 1.

The source 8 is carried in a suitable holder 11 mounted on a carriage 1 2 which is linearly moveable, as indicated by arrow 1 3 in Figure 2 in an axial direction relative to a Fresnel lens 14 fixedly mounted in the housing coaxially with the aperture 7. Any suitable mechanism, such as a rack and pinion assembly (not shown) may be provided for moving the carriage 12 as aforesaid in response to the rotation of a knob (not visible) projecting outwardly from the base of the housing. The two limit positions of the carriage 12 determine two further modes of operation of the unit, namely the flood and spot modes.The bulb is at its limit position closest to the lens 14 in the flood mode for a relatively large area of illumination and is at its limit position furthest from the lens in the spot mode, for a relatively small and well-defined area for illumination. The carriage 12 also carries a curved reflector 1 7 for reflecting the rearwardly directed light from the bulb forwardly toward the lens 14.

With reference to Figures 2 to 4, between the lens 14 and the front wall 6 is arranged a diffuser assembly 1 8. The assembly comprises, basically, a plurality, (in this case three) of rectangular diffuser plates 1 9 and a mechanism by which the plates can be selectively positioned in front of the lens 14 to constitute a light diffuser, thereby to permit rapid and easy change-over from the hardedge spot mode, in which the light passes uninterrupted from the lens 14 through the aperture 7 to the soft light mode.

Each diffuser plate 1 9 is located by a pair of end pieces 20 which accommodate the respective ends of the plate in a loose-fit manner, and which are formed with upper and lower laterally projecting bifurcated guides 21,22 respectively. The plates are constrained to move vertically in front of the lens by the co-operation of the guides 21, 22 with respective pairs of vertically extending parallel guide rails 23, 24, 25, as shown in Figure 3 and which project inwardly of the housing relative to the side walls thereof.

The two sets of guide rails on opposite sides of the housing may each be provided by a triple rail track fixed to the inside of the respective housing side wall. The plates accordingly move in respective parallel planes, spaced axially of the lens in accordance with the spacing of the guide rails 23, 24, 25. This spacing, which produces a staggered arrangement of the plates in their operative position, as shown in Figure 3, permits the plates to stack horizontally beneath the aperture of the lens 14, as shown in Figure 2, where diffusion of the projected light is not required, to produce the hard edge spot mode.

The forward plate, guided on the forward guide rails 23, is mechanically coupled by suitable means 26 projecting laterally from the upper ends of the end pieces 20 to a pair of endless chains 27, each passing round upper and lower sprocket wheels 28, 29 respectively, and disposed laterally of the lens aperture within, and on respective sides of the housing. The upper sprocket wheels 28 are co-axially interconnected by an axle 30 extending horizontally across the housing above the lens aperture between a bearing 31 and a clutch mechanism 31 a carried on opposite sides of the housing. One of the lower sprocket wheels 29 is carried on a drive shaft 32 which projects through a side wall of the housing and which also carries, outwardly of the housing, a manually rotatable knob 33; the other lower sprocket wheel merely idles.

The end piece 20 carrying the intermediate plate, guided on the intermediate guide rails 24, are each formed with lifting bars 34 projecting forwardly from their upper ends. As can best be seen in Figure 3, these bars serve to suspend this plate from the forward plate by engagement on the lower guides 22 of the forward plate end pieces 20. The end pieces 20 carrying the rear plate are similarly provided with lifting bars 35, by which this plate suspends from the intermediate plate.

The bars 35 project into spaces between the end pieces 20 and the respective guide rails, and in the lowered position of the plates iie immediately beneath the upper guides 21 of the intermediate and forward plate end pieces.

When change-over from the hard edge spot mode to the soft shadow mode is required, the knob 33 is rotated clockwise thereby causing the forward runs of the chains 27 to travel upwardly and thus lifting the forward plate. As this plate continues to rise its lower guides 22 engage the lifting bars of the intermediate plate, which is thereafter lifted. By the same process, the rear plate is lifted, and the plates eventually reach their operative positions. During this process, backward slip of the chains between successive increments of rotation of the knob 33 due to the weight of the plates is prevented by the clutch 31 a, which, however, permits the chains to move when driven by manual anti-clockwise rotation of the knob 33 to return the plates to their lower stacked position, to return to the hard edge spot mode.

The diffusion effect of the plates is produced by the formation of an array of lenslets 36 on the rear plate surfaces facing the lens 14. These lenslets, which are convex outwardly of the plates may be individual elements adhesively fixed to a flat plate surface, or preferably integrally formed with the plate. The plate and lenslets may be of suitable optical glass. The convex surfaces of the lenslets are aspherical and are designed to achieve the particular degree of light diffusion required. Also, to minimise undesirable attenuation of the light intensity, which would be produced by the ineffective areas in the array between circular or part-circular lenslets, square lenslet portions are used which interfit exactly.

It was found that this diffuser is most effective when the other optical components are in the spot mode described earlier.

The above-described lighting unit affords the significant advantage of rapid and easy changeover between the above-described modes of lighting.

Claims (9)

Claims

1. A lighting unit comprising a housing, a light source disposed within the housing, an optical system for projecting light from the source through an aperture of the housing, a diffuser having a planar array of lenticular surface elements for diffusing the projected light so as to provide a soft shadow lighting effect, and an arrangement for selectively positioning said diffuser in or out of the path of the light travelling from the source through said aperture.

2. A lighting unit according to claim 1 wherein the diffuser comprises a plurality of diffusion plates, the said arrangement being operable to position said plates in parallel, unregistered, mutually adjacent relationship across said path.

3. A lighting unit according to claim 2 wherein the plates are constrained for movement to their light diffusing positions from inoperative positions in which they mutually stack, or substantially overlap out of the said light path.

4. A lighting unit according to claim 3 wherein the said arrangement includes a drive mechanism in which a manually driven chain is arranged to drive the plates between their respective positions in 'and out of said light path.

5. A lighting unit according to claim 4 wherein a first one of the plates is coupled to be lifted by the chain and the other plates are arranged to suspend, one beneath the other, from the first plate.

6. A lighting unit according to any preceding claim wherein, said lenticular surface elements comprise convex surface portions which, in the light diffusing position of the diffuser, face inwardiy toward the optical system.

7. A lighting unit according to claim 6 wherein said convex surface portions are aspherical.

8. A lighting unit according to any preceding claim wherein the optical system includes a Fresnel lens mounted between the light source and the diffuser, and wherein the light source is displaceable axially of and relative to the Fresnel lens for adjustment of the unit between spot and flood modes of lighting.

9. A lighting unit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.