Optical: systems and elements – Absorption filter – Sequentially additive
Reexamination Certificate
2002-09-30
2004-02-03
Dunn, Drew (Department: 2872)
Optical: systems and elements
Absorption filter
Sequentially additive
C359S885000, C359S889000, C359S890000, C362S281000, C362S321000, C353S084000
Reexamination Certificate
active
06687063
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical system and components therefor for creating coloured fields of light.
BACKGROUND
In a continuously variable light beam coloration system, it is desired to change continuously the hue and saturation of the colour of a light beam in a fashion that renders the entire field to be evenly coloured for all degrees of light intensity. It is desired that the gamut of colours attainable by such a system cover as large an area of the 1931 CIE chromaticity diagram as possible. Furthermore it is desired that the intensity of the resulting colour field shall be independently controlled.
Systems that attempt such a result exist. It has been found that an acceptable range of colours can be obtained by combining three subtractive tristimulant colour filters in varying degrees. In high intensity light projectors such as are used for example in the entertainment and architectural lighting industries, the brightness of the light sources required is too high to use absorptive colour filters for colouring the light beam. So called dichroic filters are used instead which reflect the complementary colour of colour passed through the filter. Such filters display an extremely small absorption and are able to withstand the high ambient temperature and high intensity light throughput which are characteristic of such projectors. However such filters are expensive. A common configuration of such a subtractive tristimulant colour mixing system uses three filters, coloured cyan, magenta and yellow (CMY colour mixing). A further refinement may use a colour temperature correction filter (CTC) in addition which can be used to increase the gamut of available colours, but more particularly is used to vary the colour temperature of white light output. Any set of primary colours could be used to perform such colour mixing, however conventionally red, green, blue colour filters (RGB) are the only alternative to CMY actually used. Any reference in the following text to CMYC filters is equally applicable to any set of primary colour filters (plus CTC) and it is assumed that such alternatives are incorporated in any claims made.
Theoretically, any colour can be produced by combining the CMY filters to a varying degree. As an example, should a pale green colour be desired, a combination of cyan and yellow filters would be used to partially cover the output from a white light source. The degree to which the aperture is partially filled by a particular filter (and thus the degree of paleness of the colour attained) is the parameter known as the saturation. For example (theoretically) a fully saturated red would be achieved by the addition of fully saturated magenta in combination with fully saturated yellow. In practice due to the characteristics of dichroic filters, fully saturated colours are difficult to achieve by the addition of two subtractive colour filters. It is common in addition to the CMY filters to have a conventional colour wheel with red, green and blue filters mounted thereupon to achieve full saturation of these colours.
When mixing CMYC filters, it is essential that the level of saturation of a particular filter be evenly distributed across the field otherwise a mosaic or bands of colours rather than a mixture will be achieved.
The above filters are used in various light projection systems. Two principal methods are used to project light, each one having its respective advantages and disadvantages. Referring to
FIG. 1
, the condenser system provides the simplest system for evenness of lighting across the beam (flat field) and for projection purposes, however at the cost of efficiency and weight of the lens system. A substantial amount of the light output from the source is not transmitted via the projection lens, and this constitutes a loss in efficiency. Optics such as these are used when brightness is not as much a priority as image projection quality.
The most efficient (brightest for a particular light source) type of light directing system is the elliptical reflector system. This places the source at one focus of the ellipse and thus forms an image of the source at the other. It is common to place the CMYC filters as close to this second focus point as possible in order that the filters may be as small as possible. It will be noted from
FIG. 2
that the incident light makes an angle &phgr; with the filter &phgr; naturally being dependent on from where in the source the light was emitted). It will also be noted that when the filter is placed at the focal point of the ellipse, the radial distribution of the light incident on the filter matches the radial distribution of the source. The intensity at the centre of the beam is thus significantly larger than on the periphery (this phenomenon is also termed the hotspot). Further useful observations about the two above optical systems that are pertinent to colour mixing systems, concern the characteristics of the source itself. For most applications, highly efficient discharge light sources are employed. These are brighter and give out less infra-red radiation then their more conventional halogen (filament) counterparts. Also, because light is produced at an arc gap, the source of light is smaller and thus behaves more like a point source which renders the optical system more efficient. However, the light that is incident on the colour filter has spectral and as well as intensity dependence on r, &thgr;, and &phgr; (see FIGS.
1
and
2
). The effect is greatly reduced in condenser optics systems as &phgr; is small in this case. If one is to a design a coloration system that is applicable to both optical systems certain conditions have to be fulfilled, and one comes to the following conclusion. If a certain percentage saturation of a particular filter is required, then ideally one needs to colour the same percentage for each of the components of incident light passing through the coloration system; moreover, that coloured portion needs to be evenly distributed over the range of each spherical component—radial angle (&thgr;), radial distance (r) and azimuth (&phgr;).
Having satisfied this condition, we will see that an even distribution of saturation is achieved across the entire field. This will then mean that the necessary conditions for varying intensity are necessarily also met. However, it is particularly desirable to provide a system which will permit the elliptical reflector system to function both in a projection (profile) environment and in a floodlighting (wash) environment.
The geometrical relationship shown in
FIG. 3
a
relates to the use of an elliptical reflector system for projection purposes. The image to be projected (frequently of the gobo type which is a profiled cutout in an opaque material) has to be placed at the location where the cross section of light is smallest in order that maximum use is made of the light flux available. The ray path following the image has to held free of optical abberations, because a projection lens must create a high quality projected image at the intended image plane. This means that the filtering system for changing hue, saturation, and intensity may advantateously be placed in the ray path preceding the image. In order that the filtering system does not become unwieldy, the cross section of the light flux at the filtering system must not be too large. This in turn means the individual rays display a range of azimuth angle &phgr; which is larger than in known condenser systems, and for this reason the improved filtering systems must be adopted.
The geometrical relationship shown in
FIG. 3
b
relates to the use of an elliptical reflector system for floodlighting or wash purposes. In this type of use, the filters, including various effects not covered by the present application, have to placed at the location where the light flux is maximum. This location is then projected as a blurred image at a remote location by means of a short-focus projection lens incorporating a diffuser. In order that such a floodlight may be as small as possible, the ell
Glavind Mads
Rasmussen Niels Jorgen
Boutsikaris Leo
Dunn Drew
Martin Professional A/S
Skadden, Arps Slate Meagher & Flom LLP
LandOfFree
Optical system for creating colored fields of light and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical system for creating colored fields of light and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical system for creating colored fields of light and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3277173