10" is a little tall, if that's only a 2,000 lumen light. It'll be stretching like crazy, by then. Wait til it has at least one set of serrated leaves, then boost the light. I put mine under full light, right away, and never had a problem. They grow in the sun, right? It's alot more intense than any growlight, and they handle it fine. They crave it, actually. It's the heat you have to worry about, with the HPS, mainly.