An optical navigation device that regulates the brightness of an adjustable light source, and a method thereof, are described. Light from the light source is emitted onto a surface and reflected from the surface to a sensor. The light received by the sensor is used to measure movement of the optical navigation device relative to the surface. A light-sensitive device also receives light from the light source. The brightness of the light source can be adjusted according to the amount of light received at the light-sensitive device.