Daylight harvesting’s value proposition is fairly simple: As daylight levels increase in a space, electric light levels can be automatically reduced to maintain a target task light level and save energy. All automatic daylight harvesting control systems need a device that can measure light levels and signal a controller to dim or switch the lights in response to daylight contribution. This device is called a photosensor. The photosensor is a small device that can include a light-sensitive photocell, input optics and an electronic circuit used to convert the photocell signal into an output control signal, all within a housing and with mounting hardware.