Patent ID: 6454451
Filing Date: 2002-09-24
Classification: G02B

Abstract:
Flat lighting device (8, 32) havinga discharge lamp (9, 33) with a tubular discharge vessel (12) with an outside diameter D, which discharge vessel (12) defines a lamp longitudinal axis and contains an ionizable filling in its interior, a fluorescent layer (16) which covers a wall of the discharge vessel at least partially, a number of electrodes (13, 14), an aperture (17) through which light passes during operation of the lamp (9), an optical system (10; 29; 34) for spatially redistributing the light emitted by the fluorescent layer (16) of the discharge lamp (9, 33), an optical conductor plate (11; 35) of thickness d with a first narrow side (18; 36) facing the lamp (9; 33), and a second narrow side averted from the lamp, and a front side (39), an optical axis (A) lying in the plane of the front side (39) and forming a right angle with the lamp longitudinal axis, and the light from the lamp (9; 33) passing through the first narrow side (18; 36) into the optical conductor plate (11; 35), and through the front side (39) out of the optical conductor plate (11; 35), the optical system (10; 29; 34) influencing the spatial light distribution of the light which is to be, or has been coupled into the optical conductor plate (11; 35) in such a way that, seen in a cross-sectional plane of the lamp, the light distribution has at least one maximum at an angular spacing &bgr;, measured relative to the optical axis (A), the angular spacing &bgr; fulfilling the following relationship: &LeftBracketingBar;Î²&RightBracketingBar;&GreaterEqual;arctan&it;â€ƒ&it;(dL),(1)L being the longitudinal extent of the optical conductor plate (11; 35) in the direction of the optical axis (A).