The term 'light bulb unit' is composed of two words, 'watt' and 'lumen'. Watt is a unit of power, which measures the rate at which energy is consumed or generated. Lumen is a unit of luminous flux, which measures the amount of visible light emitted by a source. Together, watt and lumen are used to measure the efficiency of a light bulb, with higher wattage and lumen values indicating a more efficient bulb.