A light generating device includes: an LED module that includes a number of LED groups each of which has a number of LEDs, a memory for storing drive current for a number of LED groups respectively, an LED module driving unit for driving one of the LED groups, a current controller for controlling the drive current flowing to the LED module driving unit to drive the selected LED group, a temperature sensor for sensing heat created from the selected LED group, an operation unit for calculating the correct drive current when LEDs in the selected LED group emit light, and a key input unit for selecting one of the LED groups or a number of LED groups. The light generating device increases the light emission efficiency.