how far should 150w hps be from seedling?

[bbgun80]

I only have 150w hps for lighting, there will be a fresh sprout in a peat pellet (jiffy) inside a flat tray-for water runoff, how many inches should a 150w hps be from the fresh seedling, to promote nice roots, and healthy start?

 

[B. Friendly]

ideally you want the top of the canopy to be at your desired temp, mine is 78-82 veg. Just figure this out and adjust accordingly. I prefer this way better than a rule of thumb.
maximizes your temp and lighting

 

[daydreamer]

place your hand over the sprout under the light. if it's hot raise the light until your hand is not hot. you might consider getting a CFL light for your seedlings. then there's no worry about overheating.

 

[rlmedicals]

ideally you want the top of the canopy to be at your desired temp, mine is 78-82 veg. Just figure this out and adjust accordingly. I prefer this way better than a rule of thumb.
maximizes your temp and lighting

This post is spot on, each light is different, some can be pt closer because of less radiant heat coming from the light. as B. Friendly said just lower your light until you get your temps. in the range you would like them to be. You can probably get that 150 w light quite close, if the plant touches the light it will burn the foliage, I have used 1 150w hps and the plant was only inches from the top of the light .

 

[Synthettek]

However close you can get it, without having heat be an issue.
You never want it to get close enough to touch, or else this will be instant light / heat burn.

In my 150W Cab I have the bulb in an enclosed air-cooled reflector, which I can get pretty damn close to the canopy. The glass on the bottom of my reflector can come within 1" of the canopy with no damage or negative consequences.