How many inches should a 150w HPS be from plant tops?

How close to my plants can I put a well ventilated 150w HPS?

I am building a stealth night-stand and am debating HPS vs CFL. I already have the HPS lamp but am worried that I may only end up with 6" of room maximum between the plat top and the lamp.

Is this too close?

Some people have said the closer the better as long as you can manage the heat, but I've noticed light bleaching on my plants if lights are too close. Maybe that's only with the higher strength bulbs. I'm running a 400watter and had it about a ft. away and the tops were turning yellow so I doubled the distance and they're looking better almost overnight.

I'd probably go with the cfl's if you don't have the space for a HID.

6 inches might get a little too hot. ~1 foot is good.

The better the ventilation the closer you can position it. I used a 150 for 3 plants and it did great.

I don't know if 3-4 pc fans or a few 7in fans would be enough to keep it cool. By my estimates I would have about 6" between bud tops and the light during the end... that's pretty close.

yes it is, i have a 150w hps im usin right now n i have it 12*14" away. i might be able to move it closer but not yet there doin fine as they are.. use the cfls cuz that way to close fer ur plants. dont wanna burn those babies or run outta room.. i have cfls for side lighting also.. gluck

I ran my 150's as close as 4" and had the best growth but you need good airflow over the bulbs and plant to get that close. 6" is safer.

12" away is almost on the edge of where any useable light is left but at times I said screw it and left them that far away also just for the ease of not having to move them as often since I had a jacked up setup.
Here is a pic of what 150w lights used half way right can grow, this had two of the $20 econolights and none of the advantages of a proper grow setup, poor thing was just shoved in an open space in the closet and grown in mg soil with shultz nutes. Most of the time I did have the lights as close as possible to get it to flower this big though, the pic was on a lazy day I guess:

Notice the fans... That's how you get 4" with no burn. Notice the light sitting on a full pitcher of water... Dont' do that, I'm a lazy idiot sometimes.

This should help.

@kubrick - thanks a lot, that does help. +rep.

Considering a DIY cooltube at this point

The chart just backs up exactly what was already said showing 4" minimum and 12" max...