Sparkfun Electronics Light to Frequency Converter - TSL235R

The SFE Light to Frequency Converter - TSL235R outputs a square wave (50% duty cycle) with frequency directly proportional to light intensity (irradiance). The device has been temperature compensated for the ultraviolet-to-visible light range of 320 nm to 700 nm and responds over the light range of 320 nm to 1050 nm.