Grorite is right, general rule would be see if ur hand got hot but what if u have a different heat tolerance. I think check ur ph bro could be the start of a deficiency in my opinion as you havent stated ur environment is out in anyway. Goodluck
Umm not quite I got that last part but . I have yet to check or worry 1 I Oda about my PH since day 1, No offense of course, I know its very important and yet I have not bothered once to check on it so I doubt I will start now.
As far as the hand under the light rule goes.... Not a huge fan. I have done that dowzens of times for minutes on end to satisfy my own needs and nothing , I have the light 9" away and am sick of obsessing about finding the exact perfect height for my light , as long as my babies like it , I like it.
Environment- ummm ??? Soil ? Tent grow, that kind of thing ?