brightener

noun

1. One who or that which brightens.

   “Country air in the fields, or in gardens, when breathed at proper hours, is an excellent bracer of the nerves, and a sure brightener of the complexion.”

   “Chirol's own advice was simple: get the Russian agreement signed. March, month of change, brightener of days and moods, brought that action notably closer.”

2. A chemical agent that absorbs ultraviolet and violet light and re-emits blue light by fluorescence, used to make fabric or paper look whiter.
3. Any substance added to an electrolytic bath to yield a brighter electroplated surface.