chapter  9
24 Pages

Light Extraction from LEDs

One nds that only rays of light incident within a cone of apex angle 2ϕC, that is, the rays for which the angles of incidence ϕS are less than the critical angle ϕC on either side of the normal, are able to emerge into the epoxy lens. e cone having an apex angle θEscape = 2ϕC is, therefore, referred to as the escape cone.