<human>:  Where is spectral evidence used?
<bot>: Spectral evidence is a technique used in forensic science to determine the age of a piece of evidence. It is based on the assumption that the spectral fingerprint of a substance changes over time. For example, the color of a piece of fabric can change over time due to exposure to sunlight, so it is possible to determine the age of the fabric by comparing its color to a database of known fabrics.