The lifespan of a bulb is referred to as “Average Rated Lifetime Hours” (ARL). Incandescent bulbs generally have the shortest lifespans. The average incandescent bulb light span is approximately 750-2,000 hours. Fluorescent lights generally have a life expectancy of 10,000 to 20,000 hours and other high-intensity lamps, such as high-pressure sodium, have greater than 20,000 hours of life expectancy.