•Visible
Region
sources are:
a)Glass enclosed Tungsten
(W) filament
- normally operated at ~3000 oK with inert atmosphere to prevent oxidation. Useful from 350 nm to 2000 nm, below 350 nm glass
envelope absorbs & emission weak
b)Tungsten-Halogen lamps - can be operated as high as 3500 oK. More intense (high
flux). Function of halogen is to
form volatile tungsten-halide which redeposits W on filament, i.e., keeps filament from burning
out. Requires quartz envelope to withstand
high temps (which also transmits down to shorter wavelengths). Fingerprints are a problem – also car headlights