Screen illumination apparatus and method

DETAILED DESCRIPTION This invention offers an improved method of efficiently and uniformly illuminating a screen, such as a liquid crystal display, using a compact high-brightness source, such as the spherical plasma lamp.
One such lamp is marketed by Fusion Lamps.
The device basically consists of a central drum lens surrounding the source, a reflector situated around the drum lens, and a correcting lens at the reflector's aperture.
Referring to FIG.
1, light source 1 is situated inside protective transparent envelope 2 located in open space 2a formed by lens structure.
The entire device is circularly symmetric about a longitudinal optical axis 10.
Disposed above or forward of envelope 2 is an aspheric lens 3, with inner surface 3a and outer surface 3b.
Surfaces 3a and 3b are forwardly convex, the curvature of 3b exceeding that of 3a.
A central diverging beam is produced between edge rays 13 and 14 of the beam formed by the aspheric lens.
To the lateral side of envelope 2 is drum lens 4, with interior forwardly tapered surface 4a and outwardly convex exterior surface 4b.
Lens 4 is annular about axis 10.
It compresses the angular range of sidewards light from source 1, in that rearwardmost and lateral ray 23 having latitude angle 33 from plane 33a is redirected into latitude angle 43 for forward reflection at 23a, by reflector 5.
Similarly, forwardmost and lateral ray 24 having latitude angle 34 from plane 33a is redirected to latitude angle 44, for forward reflection at 24a by the reflector.
This reduces the required lateral and longitudinally size of curved reflector 5, which redirects in an upwards or forward direction the sidegoing light output of the drum lens 4.
Note further that there is an annular juncture 80 between lenses 3 and 4, located to divergently refract light from the source.
See rays 13 and 24a.
Situated above or forward of the aperture of reflector 5 is correcting lens 11, with inner, typically planar but alternatively spherical, surface 12 and outer surface 12a having inner zone 6 and annular outer zone 7