Photodiodes are devices used for detecting and measuring light. Their function is similar to that of a rectifier diode and is achieved through the interaction between light and the semiconductor junction. Different models of these devices are available in the market to suit various requirements. Some models are suitable for narrow wavelength ranges of light, while others can handle a wide range. In terms of applications, some devices are suitable for detecting high-speed signals, such as in fiber-optic communications, while others can detect extremely low light levels (even single photons) and can be used in various fields, from medical imaging to distance measuring.