depending how old the plant is a red stem is usually a sign of definency.most of the time they are red for a week or so after sprouting.but if they are older then that its probally definency.honestly ur better off getting a lower wattage hps or mt light.u will be waiting longer for ur bud the weaker ur light is.go 4 the hid.way better.when the plant is older a red stem can just be the strain also.