These linear fluorescent bay lights hang from ceilings with enough space for the roughly 4-ft. long housing. They use 4-ft. light bulbs with a base type that matches the fixture ballast. Bay lights deliver bright, uniform illumination from high ceilings or open trusses to floors and work surfaces below. They mount at greater heights than other types of overhead indoor lighting fixtures to illuminate warehouses, factories, gymnasiums, hangars, big-box stores, and other large, open spaces. Mounting height (high or low bay), height of the work plane (floor or elevated surface), light distribution (narrow to wide), and lumen output are key factors for selecting a bay light.