fluorescent

Fluorescent means glowing brightly when a certain light falls on it. A high-visibility jacket in headlights, a marker pen that seems lit from within.

The physics is that the material absorbs invisible ultraviolet light and gives it back out as visible colour, which is why fluorescent things look impossibly bright. The old fluorescent tube in an office ceiling works on the same principle inside the glass. Everyday English uses the word loosely for any startling brightness, giving us fluorescent yellow and fluorescent pink. Note the spelling, which has a u after the first o and catches almost everybody.