US Patent 7108399 Light source unit

A light source unit includes a substrate mounting a plurality of light emitting diodes (LED's) for irradiating beam to an object. The substrate is formed of a material having high heat conductivity and the unit includes a chip resistor mounted on the substrate and heat generation controller for heating the substrate with heat generated in the chip resistor upon supply of power to the chip resistor. The plural LED's are arranged in the form of an array on the substrate and a plurality of the chip resistors are arranged linearly along the array of LED's.