A light sensing device has a first filter to block visible light in a light path. The light sensing device also has a first color sensor and a clear sensor, to detect light in the light path after the first filter. A light intensity calculator computes a measure of the intensity of visible light in the light path, based on a difference between (a) an output signal of the first color sensor, and (b) an output signal of the clear sensor. Other embodiments are also described and claimed.