ABSTRACT
During steady-state operation filaments of incandescent lamps are considerably hot and provide luminous flux for illumination but when it is switched off the temperature as well as the light output drops quite fast. The cooling-time of a lamp is defined as the time needed for the temperature to drop to the point where the light output of lamp falls to 10% from the steady-state operation magnitude. The operating temperatures of coiled-wire filament lamps of 6, 10, 25, 40, 60, 100, 200, 300, and 500 watts are borrowed from a previous publication and the lumen outputs are estimated here. The lumen output for each degree Kelvin fall of the temperature is calculated to locate the temperature at which lumen output has dropped to 10% as per definition of the cooling time. Lastly the expression for the cooling-time has been derived and estimated for each lamp. The numbers so obtained do match satisfactorily.
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