Oh I'll be around NFinest, as I have a Dinafem Blue Widow and DNA Genetics Kush Berry grow going at the moment. They're still young and not in bloom so I won't post pics until things start getting interesting lol.
Thanks for the compliments, I try to contribute to keep what Wretched started going, which is sharing knowledge with new and old growers. Hell sometimes I even learn something new here and there, it's a good thread.
Light bleaching would most likely occur around 3-4 inches for both MH and HPS. It also depends on what stage the plant is, and the plant's wants/needs. I don't believe a 250 is honestly powerful enough to really cause any light toxicity/bleaching issues, a 600 yeah probably a 250 more than likely nothing to worry about. I keep my light at 4 inches above the tops of my plants personally and don't have an issue. I'd be concerned about heat before bleaching/toxicity. I have AC cooled air going through my light so it keeps it nice and cool. I have a temp probe hanging 4 inches below the light to make sure my tops are around 76F - 78F. I have never seen or heard of a 250 causing light bleaching/toxicity but hey I guess it could happen, you never know. There are certain bits of. knowledge that just don't apply to a smaller light like a 250, but apply more to the bigger grows that are packing 1k plus. I personally think this is one of those things, sometimes information gets muddy. Think of the game telephone lol.
15 inches isn't using your full potential for light penetration, you could bump that up a few inches to milk as many lumens as you can. If your temp and RH% are in check, you should try it out =]. A 250 is a small light, so maximizing it's performance is key. It's like having a 4 banger car lol, you want and need to max out performance.
Phew that was a lot ha, hope this helps.