The most common light source for spectrophotometry in the visible range is which of the following?

The most common light source for spectrophotometry in the visible range is which of the following?

• A. Xenon arc lamp
• B. Tungsten lamp
• C. Halogen lamp
• D. LED array

Answer: (B)

In spectrophotometry within the visible range, you want a light source that provides a smooth, continuous spectrum across all visible wavelengths with stable intensity over time. A tungsten filament lamp does exactly this: when it’s heated, it emits a broad, continuous spectrum similar to a blackbody, covering the visible region without gaps or sharp spectral features. That consistent emission makes it ideal for reliably comparing absorbance at any wavelength in the visible. Tungsten-halogen lamps, often just referred to as tungsten lamps, include halogen gas to recycle evaporated tungsten, which helps keep the filament clean and maintains color temperature and stability over a longer service life. This combination yields dependable performance for routine photometric measurements. Other options have trade-offs. Xenon arc lamps deliver very bright, broad spectra that include the visible and near-IR, but their output can fluctuate with arc stability and warm-up, and they can require more complex stabilization and cooling. LED arrays can be used, but achieving a true, smooth, full-spectrum continuum across the entire visible range requires many LEDs and can still result in uneven spectral output. Thus, the most reliable and commonly used source for visible-range spectrophotometry is the tungsten lamp due to its smooth, stable, continuous emission in the visible spectrum.

In spectrophotometry within the visible range, you want a light source that provides a smooth, continuous spectrum across all visible wavelengths with stable intensity over time. A tungsten filament lamp does exactly this: when it’s heated, it emits a broad, continuous spectrum similar to a blackbody, covering the visible region without gaps or sharp spectral features. That consistent emission makes it ideal for reliably comparing absorbance at any wavelength in the visible.

Tungsten-halogen lamps, often just referred to as tungsten lamps, include halogen gas to recycle evaporated tungsten, which helps keep the filament clean and maintains color temperature and stability over a longer service life. This combination yields dependable performance for routine photometric measurements.

Other options have trade-offs. Xenon arc lamps deliver very bright, broad spectra that include the visible and near-IR, but their output can fluctuate with arc stability and warm-up, and they can require more complex stabilization and cooling. LED arrays can be used, but achieving a true, smooth, full-spectrum continuum across the entire visible range requires many LEDs and can still result in uneven spectral output.

Thus, the most reliable and commonly used source for visible-range spectrophotometry is the tungsten lamp due to its smooth, stable, continuous emission in the visible spectrum.