What is HOURS?
Published data for bulb design life is bulb average life based on testing a large group of one bulb type at one time; and is the amount of time (hours) passed when 50 percent (half) of the group are no longer lit.
Some bulbs in the test group may have gone out quickly while others may have continued to be lit beyond double this figure.
As this measurement is taken under perfect laboratory conditions; real world conditions are expected to be much less, and are likely to be only 50 to 90 percent of rating.
If bulb is subject to voltage higher than rated or vibration or other adverse conditions, then Bulb Life expectancy will even be less.
To increase the life of your bulb; operate bulb at the EXACT voltage that bulb is designed, and protect bulb from vibration, and try to decrease the amount of on/off cycles, and provide good cooling and heat ventilation.
filament bulbs; Bulb Life is inversely proportional to the 12th power of applied voltage so operating bulb at LESS voltage than design voltage means longer Bulb Life. On those hard to reach/replace bulbs; you can get more life out of your bulbs by using higher voltage rated bulbs, for example if your line voltage is 120 volts then buy 125 or 130 volt rated bulbs, but more energy is wasted as infrared heat (not light), so Lumens Per Watt will go down.
For best efficiency and reasonable amount of hours operate bulb near its rated voltage.
references for this page: HOURS, BULB LIFE, DESIGN HOUR, DESIGN HOURS, HOUR, LIFE HOUR, LIFE HOURS
references to this page: /HO, RE-RATE, VOLT