Products in the photodiode family are used for detection and measurement of light. Based on the interaction of light with a semiconductor junction similar to that found in rectifier diodes, devices adapted for a wide range of purposes are available. Some are adapted for sensitivity over narrow wavelength ranges, others for sensitivity over a wide range. Some are suitable for detection of high-speed signals such as encountered in fiber optic communications, others for detection of extremely low levels of light (even individual photons) with applications ranging from medical imaging to distance measurement.