Tungsten-Halogen vs. Deuterium Lamps
A UV-Vis spectrophotometer needs to deliver stable light across a very wide range of wavelengths — from the deep ultraviolet to the near-infrared. No single lamp does this well, so instruments such as the Alpha and POP series combine two complementary sources.
A note on “tungsten” vs “halogen”
These are not two separate lamps. A tungsten-halogen lamp is a single source: a tungsten filament sealed in a small envelope filled with a halogen gas. The halogen recycles evaporated tungsten back onto the filament, allowing it to run hotter and brighter with a longer life than a plain tungsten bulb. So the real pairing in a spectrophotometer is the tungsten-halogen lamp and the deuterium lamp.
Deuterium lamp — the UV source
A deuterium lamp produces a smooth, continuous output across the ultraviolet region, roughly 160–400 nm. It is the source of choice for UV measurements such as nucleic acid and protein analysis. Its emission falls off in the visible range, so it cannot cover the whole spectrum on its own.
Tungsten-halogen lamp — the visible/NIR source
The tungsten-halogen lamp provides strong, stable output across the visible and near-infrared range (about 320–2500 nm). It handles colorimetric assays and any measurement in the visible region, but produces little useful ultraviolet light.
Automatic lamp switching
Because the two sources overlap, the instrument switches between them at a crossover wavelength — typically adjustable between 340 and 410 nm, with 370 nm as a common default. During a scan the spectrophotometer changes sources automatically at this point, giving seamless coverage of the full UV-Vis range with no action required from the user.
- Need UV (190–400 nm)? The deuterium lamp does the work.
- Working in the visible range only? A visible-only model (e.g. POP-V) with just a tungsten-halogen lamp can be more cost-effective.
- Need the full range? Both lamps together, with automatic switching, cover everything.