A light source module includes a solid-state light emitter, a reflective mirror, a light integration box, and a light sensor. The solid-state light emitter is configured to emit light. The reflective mirror is configured to turn a first part of the light and allow a second part of the light to pass. The light integration box is disposed in a path of the second part of the light and has an entrance. The second part of the light passes through the entrance to enter into the light integration box and is uniformly mixed in the light integration box. The light sensor is disposed on the light integration box to receive the second part of the light.