Which lamp provides a continuous spectrum of radiant energy across the visible, near-infrared, and near-ultraviolet regions?

• A. Tungsten-filament
• B. Hydrogen
• C. Deuterium
• D. Mercury Vapor

Answer: (A)

A continuous spectrum across visible, near-infrared, and near-ultraviolet comes from a hot, incandescent source that emits thermal radiation over a broad range of wavelengths. The tungsten-filament lamp heats a filament to a high temperature, producing a smooth, continuous distribution of energy according to Planck’s law. This means it glows with all colors blended together, spanning across the visible light with extensions into the near-infrared and even small amounts into the near-ultraviolet.

In contrast, lamps that rely on atomic or molecular transitions emit light at specific wavelengths. A hydrogen or deuterium lamp produces light from electrons jumping between discrete energy levels, giving a series of sharp spectral lines rather than a smooth continuum. A mercury vapor lamp also emits at particular wavelengths corresponding to mercury transitions, resulting in pronounced lines rather than a broad, continuous spectrum.

So the tungsten-filament lamp is best because its thermal, hot-body emission creates an uninterrupted spectrum across those regions, whereas the others produce discrete spectra.