Brightness is a measure of how much light is perceived by the human eye in a given scene and it is an important consideration when selecting a DLP chipset. This is a function of the amount of light (number of photons) and its spread across the color spectrum (photon energy), as well as the varying sensitivity of the human eye across the visible spectrum. The SI unit of brightness is the lumen (see ) can help determine the requirements based on screen size and ambient light conditions.