How does stray light affect my optical density (OD) reading?
Stray light is a general term for unwanted light reaching the detector of an instrument. The effect of stray light on an absorbance reading is often an unexpectedly low OD; the absorbance measured is lower than the true absorbance of the sample. The impact is usually on linearity and is greatest when measuring ODs above 2.0-2.5. Stray light is not user-correctable and is usually not caused by user error, with possible causes including optical components like degraded excitation filters. Spectrophotometers and absorbance plate readers typically incorporate features to minimize stray light.