U.S. Philips Corporation

Henri M Boots

Dirk Jan Broer

Coen T Liedenbaum

Rifat A Hikmet

Reinhold Wimberger Friedl

Jeroen J Vleggaar

Martinus B Van Der Mark

Jeroen J Horikx

Adrianus J Berntsen

Constance J Seppen

The illumination system (1) has a substrate (2) and an active layer (3) comprising an electroluminescent material, in which the active layer (3) is present between a first, optically transparent electrode layer (5) and a second electrode layer (7). The illumination system (1) is characterized in that a light-scattering layer (28) comprising a medium having light-scattering properties is present in a forward direction (29) with respect to the active layer (3), in which the non-scattered fraction of a (collimated) light beam, when passed through the light-scattering layer (8) in the forward direction (29), is in the range between 0.05 and 0.8, preferably in the range between 0.1 and 0.5. The light-scattering properties of the medium are preferably stronger as the light is more obliquely incident, as is achieved by using birefringent particles and/or media. A very suitable light-scattering layer (28) is a (half) monolayer of TiO.sub.2 particles provided on the substrate (2), with an average size of the (spherical) particles of 0.1-1 .mu.m. The light output of the illumination system (1) is further improved by providing the edges of the substrate (2) with a reflective coating (26).

Electroluminescent illumination system with an active layer of a medium

An optical system includes comprising a polarizing element in the form of a layer which comprises an isotropic material having a refractive index n.sub.i and an anisotropic material having refractive indices n.sub.a,e and n.sub.a,o. The refractive index n.sub.i is substantially equal to n.sub.a,e or n.sub.a,o. The optical system includes a retroflector for back-reflecting the polarization component diffused in the polarizing element.

Optical system which utilizes polarized light

An illumination system (3) includes an optical waveguide (11) and a light source (9) whose light is coupled into the optical waveguide (11) via at least one end face (13) of the optical waveguide (11). The optical waveguide (11) is provided with recesses (19) which are subsequently filled up with a material which is different from that of the optical waveguide (11). One of the two materials is isotropic and has refractive index n.sub.p and the other material is anisotropic and has refractive indices n.sub.o and n.sub.e. For the refractive indices it should hold that n.sub.o or n.sub.e is equal or substantially equal to n.sub.p in order that there is separation of polarization at the interfaces between isotropic and anisotropic material. Further, a flat-panel picture display device includes such an illumination system.

Illumination system for a flat-panel picture display device

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Eindhoven, Netherlands

Henri M Boots