A customer asked us about using a dye known as an optical brightener that he was told makes a profound difference in brightening a carpet. There is truth in what he said, but given the inherent danger associated with this substance it is worth highlighting the risk.
An optical (or fluorescent) brightener is a specialized chemical that absorbs invisible ultraviolet light and re-emits it as visible light. Optical brighteners are often present in carpet shampoos and bonnet cleaning compounds. The basic science behind it is that the brightener takes in ultraviolet light and re-emits it back in the form of visible light. Thus, when this extra light is added, the surface appears brighter than it really is because it is reflecting back more visible light than normal.
The problem is that an optical brightener tends to turn yellow or brown with age. Moreover, since it is a dye, there is no reversing of this process and over time the discoloring becomes permanent. For this reason, carpet manufacturers and professional cleaners warn against carpet cleaning chemicals containing optical brighteners.