Which test is used to assess stray light in spectrophotometers?

• A. Sharp cutoff filters
• B. Didymium glass
• C. Neutral density filters
• D. Holmium oxide

Answer: (A)

Stray light is light that reaches the detector from wavelengths outside the measurement band, which can distort absorbance readings, especially at high absorbance. To evaluate how much stray light a spectrophotometer allows, you use a filter with a very sharp, abrupt cutoff. With such a filter, any light that appears beyond the cutoff is clearly stray light leaking through. Measuring this leakage gives a direct sense of the instrument’s stray-light performance.

The other options aren’t suited for this purpose. Didymium glass is a general-purpose absorption filter used for different calibrations but not specifically to test stray light. Neutral density filters uniformly reduce light across the spectrum and don’t reveal leakage at wavelengths outside the band. Holmium oxide provides known spectral lines for wavelength calibration, not stray-light assessment.