I can't see from your pic but white spots is usuallt indicitive of spider mites. turn the leaf over and look fro tiny bugs. They like to come out when the lights are off. If you can't see them try a magnifying glass. If it is spidermites use neem oil. Spray the under sides of the leaves when the lights are off and cool. you can explode your bulbs if cool liquid hits a hot bulb. Very bad. Wait two weeks and repeat to kill the eggs. Neem oil is a natural extract from a nut. I think it's a nut. It smothers the mite. Good luck