Method and apparatus for controlled emission of light from prism light guide

Claim 1

A prism light guide having a light reflecting element for reflecting light from a selected region inside said guide for refraction by said guide to a region outside said guide at a selected angular orientation with respect to said guide, the reflected light path inside said guide being characterized by a vector I in , the refracted light path outside said guide being characterized by a vector I out , said vector I in having angular orientation defined by: (a) an angle θ in measured between said vector I in and the longitudinal axis vector of said guide; and, (b) an angle φ in measured between: (i) a plane which contains said vector I in and said longitudinal axis vector; and, (ii) a line perpendicular to the selected internal light guide surface through which the light is refracted; said vector I out having angular orientation defined by: (c) an angle θ out measured between said vector I out and the longitudinal axis vector of said guide; and, (d) an angle φ out measured between: (i) a plane which contains said vector I out and said longitudinal axis vector; and (ii) a line perpendicular to the selected internal light guide surface through which the light is refracted; wherein said element is located within said guide at an angular orientation defined by: (e) an angle θ m measured between said longitudinal axis vector and a vector I m line perpendicular to and directed out of the reflective surface of said element; and, (f) an angle φ m measured between: (i) a plane which contains said vector I m and said longitudinal axis vector; and, (ii) a line perpendicular to the selected internal light guide surface through which the light is refracted; such that θ.sub.m =(180°+θ.sub.out)/2 φ.sub.m =φ.sub.in ; θ.sub.in =θ.sub.out ; and, φ.sub.in =sin.sup.-1 (n'sin((sin.sup.-1 (1/n sin(φ.sub.out ±45°)))∓45°)); where n'=n(1-cos.sup.2 θ.sub.out /n.sup.2)(1-cos.sup.2 θ.sub.out))1/2; and n is the refractive index of said light guide material.