Gee, what color light is dominant in HPS ?????? RED YOU JERK, DO NOT POST ON THIS SIGHT IF YOU ARE GOING TO GIVE STUPID ADVICE TO PEOPLE!!!!!!!!!!!!!!!!!!!!!!!!!!!! Hey kid, stay out of your room during dark cycle, even green lights do not put out only true green light, any RED or BLUE spectrum WILL disturb you dark period. Read a science book on photosynthesis and BUY A MARIJUANA GROWERS GUIDE by Ed Rosenthal, he KNOWS what he is talking about and dedicates a whole chapter on light and growing. DON'T TRUST MOST ANSWERS ON THIS SIGHT , it's just someones opinion , NOT FACT. READ THE FACTS, PLEASE, for your own good . Don't take even my word, read from a REAL BOOK.........NUF SAID