Patent ID: 8393773

Claim:
A light-guide comprising a housing defining a light-guiding optical cavity having first and second major faces, and a light source of substantially monochromatic visible light at a selected wavelength arranged to direct light into the cavity, to be guided between the major faces; wherein (a) the first major face comprises an interference film which, for light at the selected wavelength, substantially transmits such light that is incident on the film over a limited angular range and substantially reflects such light that is incident at other angles; and (b) the second major face comprises a scattering reflective material having a total reflectance of at least 85% for light at the selected wavelength incident on the surface at any angle; wherein light is emitted from the optical cavity substantially uniformly across the first major face in the form of a substantially monochromatic beam of limited angular spread and said scattering reflective material defines either a wide scattering reflective surface having a dispersion angle between about 15 degrees and about 45 degrees or a narrow scattering reflective surface having a dispersion angle of less than about 15 degrees.