The term 'light unit' can be broken down into four distinct parts: Lux (3 letters), Lumen (5 letters), Lambert (7 letters), and Phot (4 letters). Lux is a unit of illuminance, which is the amount of light that falls on a given surface area. Lumen is a unit of luminous flux, which is the total amount of visible light emitted by a source. Lambert is a unit of luminance, which is the amount of light emitted from a given surface area. Finally, Phot is a unit of illuminance, which is the amount of light that falls on a given surface area.