Standards tungsten bulb

Incidentally, these different scattering patterns explain why a car headlamp causes more scattering with a quartz-halogen bulb than with a standard tungsten filament, because of their differing wavelengths and power. 

Specific procedures for implementing Eqs. (10.1), (10.2), and (10.3) differ according to the nature of the standard source. The most common source is a black-body radiator, often approximated by a tungsten bulb. A less common alternative with some attractive advantages is a standard material which luminesces in response to laser excitation. These approaches will be addressed separately. 

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