High contrast filter for visual displays down-converting otherwise blocked radiation

Abstract

Abstract A radiation filter device is provided for utilization with visual display apparatus, such as the diffusely-emitting cathode ray tube, for contrast enhancement through substantial elimination of ambient radiation effects. This objective is attained through construction of a unique filter device comprising at least two filter elements. The filter device comprises, in cascaded, superposed relationship, a first filter element consisting of a layer or film of luminescent material having a sharp cut-off, band-pass radiation transmission characteristic disposed immediately adjacent the diffuselyemitting surface of the cathode-ray tube faceplate, a second filter element that is effectively a band-pass filter having a transmission band covering the selected band, and a neutral density filter element providing uniform attenuation to radiation of all useful wavelengths within the source emission spectrum. An anti-reflective coating may also be applied to the exit face of the filter device which is the neutral density filter.

Inventors

• 👤 D R Bolum

Bibliographic Details