Stray light in a spectrometer refers to unwanted light that reaches the detector and affects the accuracy and precision of the spectroscopic measurements. It is expressed in percentage (%). When light enters a spectrometer, it is typically split into its various wavelengths using a diffraction grating or a prism. Ideally, only the signal should reach the detector, providing a clean and accurate spectrum. However, stray light can also reach the detector, originating from various sources:

Scattered light: Light may scatter off the optical elements of the spectrometer, such as lenses, mirrors, or gratings, before reaching the detector. This scattered light can interfere with the measurement of the desired signal.

Unwanted reflections: Reflections from the surfaces of optical components can redirect light towards the detector, contributing to stray light.

Detector noise: The detector itself may produce some low-level noise signals that are considered stray light, especially if the spectrometer's sensitivity is high.

Ambient light: External light sources or ambient light in the surroundings of the spectrometer can also find its way into the optical path, contributing to stray light.