The present application relates to an illumination device having a light source module, a power supply module, a driving module, a control module and a start module. The driving module outputs a driving current to the light source module based on a power supply from the power supply module. The control module controls the magnitude of the driving current based on a first voltage signal generated by the power source module. After receiving the first voltage signal, the control module controls the driving module to steadily increase the driving current in a first stage output. After receiving the first voltage signal again, the control module controls the driving module to output a constant driving current equal to the driving current at the end of the first stage.