Filament lamps will perform to specification and give optimum life when: a) They are powered at the rated voltage from a stabilised 50 Hz AC supply. b) Ambient temperature is in the range 20°C to 25°C. c) No mechanical vibration is present. Deviations from these criteria have a significant effect on lamp life, particularly with low current filaments (<80mA). Power from a DC supply at the rated voltage can reduce the listed life by up to 50%. The effect of deviation from the rated operating voltage should be noted: 5% above will reduce lamp life by up to 50%. 5% below will significantly increase lamp life. Power consumption may vary up to ±10% compared to the listed values at the rated supply voltage. Therefore particular care should be taken when a number of lamps are connected in series. In such applications it is recommended that the rated voltage be reduced by 10% to prevent premature failure of individual lamps.
