All light energy is radiant energy. The heat component of the light is in the infrared wavelength, and is what you feel when you put your hand under the light, or when you are in the sun and you feel the warmth of the sun.
As long as your plants are not burning too much, you are dealing with the radiant heat energy from your lights in an acceptable fashion.

Thanks for that. I was also wondering, if i can keep an hid that close, stretching is minimized, but could it actually stunt a plants growth to a point where it stops growing up but out?

I'm not quite sure what you are asking me, but here are some ideas that might shed light (!) on the subject.

To me, stretching is something the plants do during the first few weeks of flower. It can be incredibly rapid height gain, sometimes a couple of inches a day, and intense light, which fosters rapid growth, intensifies the stretching. I like intense stretching

Elongation is height gain that is caused by lack of light. Plants can elongate any time that they can get taller--for some varieties, that means up until harvest; for others, only during the grow cycle and the first few weeks of flower (typical of Indicas). I avoid elongation.

I don't think you can stop a plant from growing with intense lighting. If you can get the bulb close enough without burning, you may see some buds become deformed.

If your light is on a mover, then you can still get decent coverage from a light that is extremely close. You will definitely get more (and better) bottom buds. Even if a few top buds are harmed, overall, you should benefit.

I guess what im saying is, well the plants i have now where supposed to be at least 3' tall. Not one is over 2' tall. I keep a 400watter about 8" above my canopy. I was thinking it is because of how close my light is that they didn't grow up but out. I'm growing in a very small area. I am in 6th week of flower.

In my opinion, you are lucky the plants did not get any taller. 400 watt HPS lamps make good, solid bud for only about 8 to 10 inches from the top of the plant to the lowest bud site. That's because of the rapid fall-off in light intensity, described by the inverse square law:

light intensity = 1 / distance squared

So the light intensity 16 inches from the bulb is 1/4 of the intensity 8 inches from the bulb.

If you want taller plants (why?), you may have to leave them in the veg cycle a little longer. Also, do you do a high intensity veg cycle, or one where the plants are growing slowly under fluorescents? If the plants are growing very rapidly at the end of the grow cycle, they will stretch more.

I vegged for a month under 400w mh. I just wanted to no if me having my light so close caused them to grow out instead of up. Its my understanding that my light can produce good light upto 3'... If thats the case then i could have grew my plants almost another foot and still produce good buds,,more buds..

To answer this more accurately, I need to know:

The area of the box.

Whether clones or seeds.

How long a flower cycle you plan.

In general, for high average yield, you want many, small plants, a short grow cycle, and a short (if possible) flower cycle.

Taller plants are fine for more powerful lights. For a 400 watt hps, you'll get about the same weight whether the plant is 2 or 3 feet tall, assuming the canopy fills out your flower room. The buds on the 2 foot plant will be fewer, larger, and denser.
And no, short stature was not the result of the light being too close. You could get a little bit taller plant if you used 400 watt hps in the grow cycle, instead of mh. MH lights are highly overrated--I never use them.

my room is 3'x2'x56' strain calls for 8-10 weeks flower i wanna go till its just rite. 4 plants around 20" tall 400 watt hps... I should be right on pace for 2 ounces a plant,maybe? I also read in a Rosenthal book that hps was plent fine to use from start to finish.

Sounds like a plan to me. HPS extended spectrum bulbs can veg with the best of them, lookin good... 2 oz @ is certainly doable.

Don't bother with extended spectrum HPS--I've used them, and they're a waste of money, in my opinion. Use standard, high-quality bulbs, like Philips, GE, Sylvania, etc.--NOT Hortilux or any hot-rod bulb. For 400 watt bulbs, the Home Depot ones are fine. For 600, get any bulb made in Europe.
Good luck with your project.