Optical detectors and sensors are used to measure light and optical signals. They convert light energy into electrical signals that can control other equipment or be further processed in some form. They are used in a variety of areas of science, engineering, and industry. Optical detectors and sensors can range from simple photodiodes and phototransistors to complex optical devices such as imaging spectrometers. They are also used for imaging and sensing applications such as nighttime surveillance or medical imaging. Some optical detectors and sensors require an illumination source such as an LED or laser diode. Other sensors rely solely on the ambient light in their environment. They can be used to detect a range of different optical signals, such as UV radiation, infrared radiation, visible light, and so on. Optical detectors and sensors are widely used in telecommunications, optoelectronics, aerospace, automotive, and more.