Spectrophotometry measures what type of light?

• A. Transmitted light
• B. Reflected light
• C. Emitted light
• D. Scattered light

Answer: (A)

Spectrophotometry hinges on detecting how much light passes through a sample. A beam of light at a specific wavelength is sent into the sample, and the detector measures the transmitted portion that emerges on the other side. The amount of light that makes it through relates to how much the sample absorbs at that wavelength, which is why this technique uses transmitted light (and derives absorbance from that transmitted intensity). The other options describe different phenomena: reflected light is used in reflectance measurements, emitted light comes from fluorescence or luminescence, and scattered light is the focus of nephelometry or turbidity measurements.