Illumination – Light source and modifier – Including selected wavelength modifier
Reexamination Certificate
1995-10-18
2004-08-03
Husar, Stephen (Department: 2875)
Illumination
Light source and modifier
Including selected wavelength modifier
C356S418000, C359S890000
Reexamination Certificate
active
06769792
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
The present invention relates to light projectors used for various illumination and lighting applications and in particular to projectors that are used to obtain visual effects, light pattern generation and projection in stage illumination and in architectural, display and similar applications.
BACKGROUND AND DISCUSSION OF PRIOR ART
Lighting projectors, e.g., those used in stage lighting, are typically equipped with one or more control devices for controlling intensity or focusing or dimensioning the beam, changing its color, or changing the beam's direction. Modern multiple parameter (automated) projectors include controls for all of these parameters and more.
Although such projectors perform effectively in many applications, they suffer from a number of limitations which, if overcome, could greatly expand the visual effects achievable by the lighting instruments and extend their utility to other environments. To achieve such advances, improvements are required in the beam forming mechanism, in the projection of patterns, in the management of heat associated with the light source, in the control of beam color, and in the noise levels which derive from present cooling techniques. To be effective, these improvements must function in a densely packed, compact and sometimes highly mobile structure housing both very fragile optical and electronic components together with a light source capable of producing oven-like temperatures. (An exemplary application involving a nominal image size of 10 ft. by 10 ft. (100 square feet) calls for brightness in the neighborhood of 100 foot candles thus requiring the projector to produce about 10,000 Lumens.) Moreover, certain types of lighting instruments go on “tour” and must withstand truck transport abuses and the vagaries of the weather.
A number of lighting control applications call for controllable beam shapes and patterns. Performance lighting in stage productions, for example, often requires a variety of different beam patterns and/or shapes. For this purpose, a projection gate is often used to form the desired image across the beam of light. Typically, the projection gates are embodied as shutters or etched masks that function like stencils in the beam path to project a particular beam configuration. Known arrangements, “gobos” for example, often include rotary assemblies that incorporate several pattern generating elements encircling the axis of rotation, along with a drive mechanism for rotating a selected pattern into the beam path.
In such arrangements only a limited number of patterns are available, there is no grey scale, and resolution is also limited. Another inherent limitation in this type of system, associated with its dependence on physical motion, is the rapidity with which a desired pattern can be selected and implemented.
Arrays of liquid crystal pixels are potentially useful as projection gates because of their electro-optic effect, and because a virtually unlimited number of high resolution images may theoretically be synthesized quickly and easily.
Such liquid crystal arrays can be used to create images by selectively placing each individual pixel of the array in a relaxed (light blocking) state, or in an aligned (light transmitting) state, or in a state intermediate between the two extreme positions according to a “grey scale”. Selection of a grey level may be obtained by controlling the voltage or other control stimuli that is applied to the pixel, thus controlling the alignment or transmissivity of the associated liquid crystals. Over certain ranges there is a predictable relationship between the applied control stimulus and the extent of alignment among the liquid crystals in the pixels, thus providing grey scale control. Whether used in this manner or in a two-state, on-off mode, pixellated liquid crystal arrays have the potential to be used in a “light valve” capacity to create a complete picture across a beam of light.
Pixels in an array of liquid crystals may be relatively densely packed thus offering opportunities for higher resolution and transmission efficiency. Also, they may be individually controlled by an addressing scheme capable of selectively placing each pixel of the array in a desired state. Thus a virtually limitless range of images may be rapidly varied. In many applications pixels are arranged in a row and column configuration and activated by applying a potential to a particular control element associated with each of the pixels. Alternatively, a multiplex or other addressing scheme can be employed to reduce the number of elements necessary to address the pixels. Both active and passive matrices may be utilized.
Certain types of liquid crystal arrays have been previously used with some success in image projection applications. Arrays of twisted nematic liquid crystal (TNLC) have been used and have provided several advantages over other image forming techniques. However, TNLC devices typically require pre-polarization of incident light. Since a polarizer has to be placed in the optical path to polarize the light before it reaches the TNLC gate, there is a loss of intensity of more than fifty percent before it even reaches the array. In high intensity projectors for stage lighting and the like, this loss is far beyond acceptable levels.
There have been efforts to address the light loss problem. An improved method of illuminating a TNLC light valve with linearly polarized light is discussed in “Large-screen Projection Displays II” by William P. Bleha, Jr. (S.P.I.E. Vol. 1255, 1990). The disclosed method for converting unpolarized light into linearly polarized light is said to double the intensity realized by conventional polarizers.
The disclosed polarization method uses a polarization convertor consisting of a polarizing beam splitter, a polarization direction rotator and a synthesizer to significantly improve the illumination efficiency. The polarizing beam splitter separates the incident light into two mutually perpendicular linearly polarized beams (transmitted p-polarized light and reflected s-polarized light). The polarization direction rotator effectively recaptures much of the light that was lost in previous polarizing systems by rotating the polarization direction of the p-polarized light ninety degrees to equalize both polarization directions. Thereafter, the two components of the light are combined on the liquid crystal by the synthesizer.
The polarization convertor may ultimately provide a conversion efficiency approaching 100%. However, reflection and absorption losses in the polarization convertor components, plus the losses in the contrast-enhancing sheet polarizer, presently result in an overall 20% loss of intensity as the unpolarized light is converted to a linearly polarized beam.
There are other formidable barriers in addition to excessive light loss. Conventional polarizers typically associated with liquid crystal arrays lose light intensity through an absorption process. Unfortunately, absorption converts light energy into heat causing the temperature of the gate and surrounding optics to rise to intolerable levels. In performance and display applications, where projector temperatures can reach combustible levels, this process of heat absorption causes a thermal buildup which would greatly exceed the temperature limits of the liquid crystal array.
Various cooling techniques have been proposed which have attempted to alleviate the destructive thermal effects of radiant energy absorption. U.S. Pat. No. 4,739,396 to Gilbert Hyatt, particularly columns 50 through 62 of this patent, discusses numerous cooling techniques which have been proposed for use in light projectors. See also U.S. Pat. No. 4,763,993 issued to James H. Vogeley, et al.
Cooling by forced air is thought to be effective in some applications because it is theoretically transparent to incident light and does not reduce the amount of transmission. Unfortunately however, heat dissipation techniques which depend on fan operation and other forced air cooling techniques can create nois
Carr LLP
Genlyte Thomas Group LLC
Husar Stephen
LandOfFree
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