Don't think it's wpm. Have you noticed any water drops on the leaves? Did you water shortly bevor lights off? There is a phenomenon called gutation where plants push out their juices when the pressure gets too strong. When this juice transpires, the water evaporates stuff that was dissolved in it stays their. Can you wash it or rub it off?
@organoman there are pesticides for insects "insecticide" and also against fungi they are called "fungicide"