LIGHT PATTERN GENERATOR

Abstract: A light pattern generator is utilized to produce an image which is projected onto a stage or screen. The image is de­ rived from a beam of light. The light pattern generator com­ prises a heat resistant glass plate having a reflective layer de­ posited on one surface thereof. A nonreflective layer is depo­ sited on the surface of the reflective layer. Both of the layers are etched to produce an opening extending through the lay­ ers wherein the opening has the shape of the desired image. The beam of light is directed through the transparent plate and the portions not passed through the operation are reflected by the mirror surface of the reflective layer. This prevents the buil­ dup of heat within the light pattern generator. Any extraneous light which is received at the nonreflective layer is absorbed to prevent the escape of unwanted light and its projection to the stage.

Description: TECHNICAL FIELD The present invention pertains in general to stage lighting and in particular to such lighting which involves the projection of a silhouette of an image on a stage, screen or backdrop. BACKGROUND OF THE INVENTION There are many aspects to providing stage lighting. These include spotlights, flood lights, colors and moving lights. A significant aspect of such stage lighting is the projection of images, in the form of a silhouette, onto the stage to a backdrop, screen or to the performers themselves. The conventional light pattern generator for projecting such a silhouette image is termed a "gobo". The typical gobo is made of a sheet of metal which has the desired image cut in the sheet as an opening for shaping a light beam (US-A-4 392 187). The metal sheet, with the cut-out image, is placed in the beam from a spotlight so that the portion of the beam that passes through the sheet is shaped to correspond to the image cut in the gobo. The image is typically passed through a lens so that the image can be focused on a desired portion of the stage. The gobo is mounted directly in the beam of light. Since stage lighting uses intense light beams, the gobo can become very hot. In fact, it is not unusual for a gobo to become so hot that it begins to glow with a cherry red color. To combat the extremely high heat, gobos have been fabricated of heat resistant metals, such as stainless steel. However, even gobos made of this material have a relative short lifetime and require frequent replacement. The conventional gobo is also limited as to the configurations that can be produced. Since all of the metal elements of a gobo must be supported, there must often be unwanted support members included in the design. As an example, it is impossible to produce a complete ring design because support members must extend from the exterior to support the interior metal. Therefore, in view of the need for the projection of images as a part of stage lighting and the short lifetime of conventional gobo image producers, as well as the limitations on designs, it is an object of the invention to provide for a light pattern generator which can project a desired image, while at the same time withstanding the high temperature present within a light fixture. Such objective is achieved by means of a light pattern generator for projecting an image by means of a light beam, comprising: a transparent plate for placement in said light beam, which plate has an image forming area; and a light reflective layer bonded to a surface of said transparent plate and leaving an opening in the shape of said image for passing a portion of said light beam therethrough to produce a beam in the shape of said image, the portion of the light beam striking the transparent plate outside said opening being reflected by the reflective layer. The light pattern generator according to the invention comprises a light reflective layer with an opening in the shape of the image through which a portion of the light beam can pass since the plate is a transparent plate. The light reflective layer reflects the remainder of the light beam to prevent heat buildup in the light pattern generator. Compared to conventional gobos the light pattern generator according to the invention is quite small and can be easily fitted on a wheel to produce a large number of image shapes in a very compact space. Any desired image shape can be produced without the limitation of support members for holding interior blocking members in place. The invention further relates to a lamp fixture for projecting an image by means of a light beam comprising: a housing; light generating means mounted within said housing for producing said light beam; a light pattern as defined above and located within said housing; and a first lens mounted in said housing on the opposite side of the light pattern generator from said light generating means. Lamp fixtures with transparent plates are known per se (DE-U-1 904 008). However, such lamp fixtures are not structured for projecting an image by means of a light beam but only to generate light of different colours. They are to be used in homes and contain a'conventional light bulb the light of which passes through differently coloured glass plates or the like mounted on a rotating disk. In such type of lamp fixtures the problem outlined above does not exist since the heat development is quite small and does not constitute any serious problem. BRIEF DESCRIPTION OF THE DRAWINGS For a complete understanding of the present invention and the advantages thereof, reference is now made to the following Description taken in conjunction with the accompanying Drawings, in which: FIGURE 1 is a perspective illustration of a lamp fixture having a light source, a light pattern generator and a lens for producing a beam having a desired image shape, FIGURE 2 is a light pattern generator, as shown in FIGURE 1, which has a desired image formed by layers on the surface thereof, and FIGURE 3 is a sectional view of the light pattern generator shown in FIGURE 2 together with ray lines which illustrate the transmission, reflection and absorption of light by the light pattern generator. DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGURE 1 there is illustrated a light fixture 10 which can be used for the purpose of stage lighting. The fixture 10 has a housing 12 which serves to support and enclose the components of the fixture. Within the housing 12, the fixture 10 has a light assembly 14 which comprises a reflector 16 and a bulb 18. This assembly produces a collimated light beam 20 which is transmitted to a lens 22 which serves to focus the beam. A pattern wheel 24 is mounted for rotation by a stepper motor 26. Around the periphery of the pattern wheel 24 there are provided a plurality of light pattern generators, such as 28. In the disclosed embodiment each of the generators 28 has a trapezoidal shape to form, as a group, a concentric ring about the periphery of the pattern wheel 24. The generator 28 is provided with a transparent opening 30 which is in the shape of a desired image that is to be projected toward the stage. The pattern wheel 24 can be provided with a plurality of light pattern generators, such as 28 and it can further be provided with color filters for producing different colors for the light beam produced by the fixture 10. Any one of the desired images or colors can be rotated by the motor 26 such that the appropriate color filter or light pattern generator is positioned within the light beam. The light beam is focused by the lens 22 such that it is sufficiently small to pass through the light pattern generator 28. The beam then expands and is passed through a lens 32. The lens 32 serves to provide focusing for the beam and makes the beam essentially colinear. If necessary, the lens 32 can be moved forward or backward in the fixture 10 to focus the image produced by the beam at any desired distance. The light beam which passes through the lens 32 is directed onto a stage to produce an image 34 which is in the shape of the opening 30 in the light pattern generator 28. The disclosed embodiment shows the opening 30 to be in the shape of a 5-point star which in turn produces an image 34 which has a corresponding star shape. The light pattern generator 28 is further illustrated in FIGURES 2 and 3. As noted above the generator 28 has a trapezoidal shape such that a plurality of such generators, and corresponding color filters, can be placed edge to edge about the periphery of the pattern wheel 24 so that there is neither blocking of light or the escape of white light between the adjacent ones of the pattern generators or color filters. The pattern generator 28 comprises a transparent plate 40 which has bonded to the surface a reflective layer 42, which is positioned on the surface of the pattern generator 28 opposite from the light assembly 14. The reflective layer 42 has a mirror finish for reflecting light which strikes the layer. Facing in the direction opposite from the mirror surface of the reflective layer 42 there is provided a nonreflective layer 44 which serves to absorb light which strikes the layer. The layers 42 and 44 are provided with the opening 30 which is in the shape of the desired image. The opening 30 extends through the layers 12 and 44, but does not extend through the transparent plate 40. The light pattern generator 28 is shown in a section view in FIGURE 3. The lenses 22 and 32 are further shown in FIGURE 3 together with various light rays which illustrate the transmission, reflectance and absorption of the various portions of the light beam 20 which is produced by the light assembly 14. As noted above, the light pattern generator 28 comprises a transparent plate 40 which has a reflective layer 42 bonded to the surface thereof on the opposite side from the 22. The surface of the layer 42 facing the lens 22 is a mirror surface which reflects the light that strikes the surface. The layer 44 is bonded to the surface of the layer 42 and has an exposed surface which faces the lens 32. The exposed surface of the layer 44 is light absorbent and is therefore nonreflective. The opening 30 extends through both of the layers 42 and 44 and permits light to pass unimpeded through the generator 28. The beam which passes through the light generator 28 is conformed to the shape of the opening 30. The light pattern generator shown in FIGURE 3 has a trapezoidal shape. For the disclosed embodiment, the base length is 20.3 mm (0.8 inch), the sides are 38.1 mm (1.5 inches) and the top is 44.5 mm (1.75 inches). The plate 40 has a preferred thickness of 1.0 mm (0.04 inch). Operation of the light pattern generator 28 is now further described in reference to FIGURE 3. The light beam 20 is focused to a smaller diameter by the lens 22 at the region of the light pattern generator 28. Portions 46 of the light beam 20 are reflected by the mirror surface of layer 42 away from the pattern generator 28. Portion 48 of light beam 20 passes through the opening 30 and is in the shape of the opening 30. The portion 48 of the beam 20 is directed to the lens 32 and refocused to be an essentially collimated beam which produces the image 34 at the desired location on the stage. Portions 50 of the light beam 20 are reflected back from the lens 32 as well as from the interior surfaces of the housing 12. The portions 50 which strike the nonreflective layer 44 are absorbed in the surface of layer 44. Should the portions 50 be allowed to reflect back from the light pattern generator 28 into the lens 32, these portions of light will produce spurious images which interfere with the desired image 34. Therefore, the light reflected within the housing between the light pattern generator 28 and the lens 32 is absorbed at the surface of layer 44 to prevent the directing of any interferring light rays through the lens 32 toward the image 34. Should any portion of the extraneous light between the light pattern generator 28 and the lens 32 be directed through the opening 30, it will either be dissipated in the housing 12 or redirected through the opening 30 in the correct shape of the beam. The method of manufacturing the light pattern generator 28 is now described in reference to FIGURE 3. The process begins with a large sheet of the transparent plate 40. The plate 40 is preferably made of PYREX glass and has a thickness of 1.0 mm (.04 inch). On one surface of the plate 40 there is deposited a layer of positive photo resist which is in the shape of the desired image. On the surface of the photo resist there is then deposited a layer of aluminum having a thickness of approximately 2,000 Angstroms. There is then deposited on the surface of the aluminum a multilayer dielectric coating which comprises a plurality of layers which together have a thickness of approximately 2,000 Angstroms. The multilayer dielectric coating consists of alternating high and low index refraction materials which form an interference filter which functions as a "black mirror", which is a nonreflective surface that absorbs light. Examples of materials that have the high and low index of refractions are magnesium flouride and zinc sulfide. The plate with the various coatings is then exposed to acetone which dissolves the photo resist and lifts all the layers of material which were deposited immediately over the photo resist. The acetone has no effect upon the glass. As a result, there is produced an opening through the deposited layers which is in the desired shape of the image. This process is carried out concurrently on a large sheet of the material which comprises plate 40. Lines are scribed across the glass sheet which includes the plate 40. The sheet is then broken along the scribed lines to produce the individual light pattern generators, such as generator 28. In the preferred embodiment of the present invention, the layers 42 and 44 are on the same side of the plate 40, however, it would be equally functional to have the layers on opposite bides of the plate 40, but this would require each layer to be etched separately. In operation, the light pattern generator 28 passes a portion of the light beam 20 to produce the desired image. The reflective layer 42 reflects in excess of 95% of the light that strikes the layer thereby preventing most of the light from being absorbed by the light pattern generator 28, which would otherwise tend to create heat. The light fixture 10 is provided with air ventilation, not shown, which cools the generator 28. The relatively low amount of heat absorbed by the generator 28 permits it to be cooled by forced air cooling. By keeping the generator 28 at a relatively low temperature, it has a much greater lifetime than the conventional metal design for gobos. The layer 44 serves to absorb light, but the amount of this secondary reflected light is quite small and the actual heating which is generated by the absorption of light by layer 44 is very small.

Claims: 1. A light pattern generator (28) for projecting an image (34) by means of a light beam (20), comprising: a transparent plate (40) for placement in said light beam (20), which plate (40) has an image forming area; and a light reflective layer (42) bonded to a surface of said transparent plate (40) and leaving an opening (30) in the shape of said image (34) for passing a portion (48) of said light beam (20) therethrough to produce a beam in the shape of said image (34), the portion (46) of the light beam (20) striking the transparent plate (40) outside said opening (30) being reflected by the reflective layer (42). 2. The light pattern generator as recited in Claim 1, including a light nonreflective layer (44) supported by said transparent plate (40) and having an opening therein corresponding to said opening (30) in said reflective layer (42), said nonreflective layer (44) facing away from said light beam (20) for absorbing extraneous light (50) which strikes said nonreflective layer (44). 3. The light pattern generator as recited in Claim 2, wherein said transparent plate (40) is heat resistant glass, said light reflective layer (42) is aluminum and said light nonreflective layer (44) is a multilayer dielectric coating. 4. The light pattern generator as recited in Claim 2, wherein said light nonreflective layer (44) is bonded to a surface of said light reflective layer (42). 5. The light pattern generator as recited in Claim 4, wherein said layers (42, 44) are positioned on a surface of said transparent plate (40) opposite from a surface of said transparent plate (40) which receives said light beam (20). 6. A lamp fixture (10) for projecting an image (34) by means of a light beam (20) comprising: a housing (12); light generating means (14) mounted within said housing (12) for producing said light beam (20); a light pattern generator (28) comprising the features of Claim 1 and located within said housing (12); and a first lens (32) mounted in said housing (12) on the opposite side of the light pattern generator (28) from said light generating means (14). 7. The lamp fixture as recited in Claim 6, wherein said transparent plate (40) has a light nonreflective layer (44) facing said first lens (32) for absorbing extraneous light (50), said light nonreflective layer (44) having an opening therein which matches the opening (30) in said light reflective layer (42). 8. The lamp fixture as recited in Claim 7, wherein said light nonreflective layer (44) is positioned on a surface of said transparent plate (40) which is opposite that of said light reflective layer (42). 9. The lamp fixture as recited in Claim 7 or 8, wherein said transparent plate (40) is heat resistant glass, said light reflective layer (42) is aluminum and said light nonreflective layer (44) is a multilayer dielectric coating. 10. The lamp fixture as recited in Claim 6 or 7, wherein said layers (42, 44) are positioned on a surface of said transparent plate (40) opposite from a surface of said transparent plate (40) which receives said light beam (20). 11. The lamp fixture as recited in one of Claims 6 to 10, comprising a second lens (22) mounted within said housing (12) between the light pattern generator (28) and said light generating means (14) and focusing said light beam (20).

Inventors: BORNHORST, JAMES M.
Applicants: VARI-LITE, INC.(A DELAWARE CORPORATION)
Application year: 1987
Main classification: F21P5
IPC codes: G03B21, F21S10, F21S8, G03B15