Very slow growth: external temperatures are still low (min 5-8°, max 14-17°), and the grow box sits in an unheated room outside the house. The lamp, when turned on, raises the temperature just above 20-21° in the box, but when turned off in the early afternoon, it drops around 16°. I think I'll move to a 20/4 light cycle to reduce the cold, at least for the coming week. Spring is coming, by the way, so in the future the external temperature will be higher.