A light therapy device includes a number of light emitting elements, a detection module, a determination module, and a control module. The detection module is configured to detect a body parameter of a human body. The determination module is in communication with the detection module and configured to receive the body parameter and output a fatigue level corresponding to the body parameter. The control module is in communication with the determination module and the light emitting elements. The control module is configured to receive the fatigue level and control the light emitting elements to emit lights with an irradiation intensity for a preset period of time in response to receiving the fatigue level. The irradiation intensity and the preset period of time have a predetermined relationship with the fatigue level.