Incandescent Lamp from Black Body Perspective

Abstract

The incandescent lamp from black body perspective was investigated using commercial lamps of various watts. The major component of the incandescent lamp is the tungsten filament. The resistance of the tungsten filament was measured using a digital multimeter at an initial laboratory temperature. Light produced from lamp was separated into visible colours by an equilateral triangular glass prism. Deduced resistances were used to obtain equivalent temperatures by power-law parameterization. The Wien’s displacement law was used to estimate Peak wavelengths at different temperatures. The diameter of the tungsten was measured after dissecting the lamp, and this was used to determine its cross-sectional area. Both Wien’s displacement law and Stefan-Boltzmann expressions were applied in determining the filament’s spectral emissive power (SEP) in comparison with that of the visible spectrum. Planck’s graph of intensity using peak wavelength of tungsten filament as reference was juxtaposed with the intensity of visible spectrum using OriginPro 2016 SR0 b9.3.226. The maximum temperature attained was 2852.87 K with (SEP) of 1478955.24 Wm-2 for the 200W lamp. For the 100W lamp, the (SEP) obtained was 749347.9078 Wm-2 at 2489.14 K. Both temperatures, and even as low as 1250 K, were in agreement with Wien’s displacement law. The percentage estimation of visible spectrum in the radiation was about fourteen percent (14 %) while the rest was infra red radiation. This low visible light produced may be as a result of the non-ideal black body nature of the tungsten filament; and so, the incandescent lamp may be considered a quasi-black body.