Except where special circumstances exist, Federal agencies must maintain illumination levels at—

(a) 50 foot-candles at work station surfaces, measured at a height of 30 inches above floor level, during working hours (for visually difficult or critical tasks, additional lighting may be authorized by the Federal agency buildings manager);

(b) 30 foot-candles in work areas during working hours, measured at 30 inches above floor level;

(c) 10 foot-candles, but not less than 1 foot-candle, in non-work areas, during working hours (normally this will require levels of 5 foot-candles at elevator boarding areas, minimum of 1 foot-candle at the middle of corridors and stairwells as measured at the walking surface, 1 foot-candle at the middle of corridors and stairwells as measured at the walking surface, and 10 foot-candles in storage areas); and

(d) Levels essential for safety and security purposes, including exit signs and exterior lights.