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2017 | 15 | 86-97
Article title

Heating-times of tungsten filament incandescent lamps

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Electricity provides power to incandescent lamps to heat the filament hot enough so that it provides light for illumination. The time taken to achieve a state of full brilliance after being turned on is so fast that it may be presumed to be adiabatic, hence it is deemed adiabatic heating time. In view of the fact that in actual practice simultaneously black-body radiation cools the filament, the General Electric in its bulletin provides a better time scale describing heating and cooling of filament. These are average times required for the filament to warm up to 90 per cent light output after the circuit is closed, or to cool down to 10 per cent after the circuit is opened, respectively. The exercise of estimating luminous flux and heating-times for typical 10, 100, 500 and 1000 W lamps have been undertaken for the first time for the benefit of students. This problem involves three disciplines electricity, optics and heat. The first describes the power needed to heat the filament quickly, optics then helps us in determining the light output and discipline of heat provides methods for solving the heat equation in order to estimate time to light or time to darkness. The study reveals that the supposition of linear configurations for the filaments neither matches luminous flux nor the heating-times. HS Leff’s suggestion of introducing a shadow factor which reduces the exposed surface area, as it so happens in the coiled filaments, successfully explains the measured observations.
Physical description
  • Department of Farm Engineering, Banaras Hindu University, Varanasi 221005, India
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  • [15] D. C. Agrawal, Cooling-times of tungsten filament lamps, World News of Natural Sciences, 13, 52-62 (2017)
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