Filament lamps will perform to specification and give optimum life when: they are powered at the rated voltage from a stabilised 50Hz ac supply; the ambient temperature is in the range +20°C to +25°C; and where no mechanical vibration is present.

Deviations from these criteria can have a significant effect on lamp life, particularly with low current filaments (<80mA).

Operation from a DC supply at rated voltage can reduce specified life by up to 50%. The effect of variation 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. Current consumption can vary by up to ±10% on stated values at rated supply voltage. Care should therefore be exercised when running a number of lamps in series. In such applications it is recommended that the rated voltage be reduced by 10% to prevent premature failure of individual lamps.

Conversion of light output units: Lumens = MSCP x 12.6, MSCP = Lumens / 12.6.