Patent ID: 7486342

Claim:
A back projection screen including a layered optical element having variable optical properties, comprising: a first layer, said first layer being one of glass, a rigid substrate based on a polymer of polycarbonate, and a flexible polymer material; a first and a second thermoplastic polymer sheet layer, said first thermoplastic polymer sheet layer in contact with the first layer; (a) variable light scattering system, of optical-valve or liquid-crystal system type, a suspended-particle system or a holographic or thermotropic system, said variable light scattering system (a) sandwiched between the first and second thermoplastic polymer sheet layers; a second layer, said second layer being one of glass, a rigid substrate based on a polymer of polycarbonate, and a flexible polymer material, said second layer in direct or indirect contact with the variable light scattering system; and at least one element antireflecting in the visible range, wherein at least one of said first and second layers comprise (b) an absorbent element, absorbing light at least in the visible range and chosen from at least one of the following elements: a plastic rigid substrate, a bulk-tinted glass, a bulk-tinted sheet of flexible polymer of thermoplastic type, a plastic film configured to be calendered to a rigid substrate, or a thin absorbent layer placed on one of a face of a glass or plastic rigid substrate or of a sheet of flexible polymer, and the back projection screen does not include a power source for the absorbent element, and the back projection screen does not include an electrochromic material.