Patent ID: 7122946

Claim:
A light source device comprising: an electric discharge tube containing mercury therein and having electrodes at both ends thereof; and a heat conducting path in contact with a part of said electric discharge tube; wherein the following relationship is substantially satisfied: 6×10 −5 ( m 2 ·k )/ S< (1/ k 1−1/ k 2)W (1) where a part of said electric discharge tube in contact with said heat conducting path is defined as a cooling part, a part of said electric discharge tube not in contact with said heat conducting path is defined as a non-cooling part, a cross sectional area of the interior of the electric discharge tube is defined as S (m 2 ), an amount of generated heat per unit length of said electric discharge tube is defined as W (W/m), heat conductivity from inside to outside of the tubes per unit length in the longitudinal direction of said non-cooling part is defined as k1 (W/K/m), and heat conductivity from inside to outside of the tubes per unit length in the longitudinal direction of said cooling part is defined as k2 (W/K/m).