US Patent 7766519 Illumination devices with cooling fans and cooling methods thereof

Methods for cooling an illumination device are disclosed. The illumination device comprises a cathode, an anode and a cooling fan. A variation of a lamp voltage of the illumination device is first detected. The lamp voltage is the voltage difference between the cathode and the anode, and the variation of the lamp voltage is derived from comparing the lamp voltage which is detected with the lamp voltage at the first time the illumination device is used. A rotational rate of the cooling fan is then adjusted according to the variation of the lamp voltage.