how far does a 400w mh go?

can anyone tell me from experience how far should my 400w mh be from my plants?
i have one hugs one and two small ones , there all the same height
i also have four t8's on the wall for side lighting

poot your hand on top of your plant and see how hot it is and ajust it to where it is as close as you can get it with out it burning your plant . I poot my MH any where from 6 to 12 inches from my plant . You want to get it as close as you can get it so that your plants get the most light out of your light to far way and the only part of your plant that will get light is the top .Just make sure that your plant dont get to hot or you will have more problems .Let me know how it works out for you .and if you have any mor3e qustions let me know

Usually 1' to 2' is OK. I go for 1' but keep an eye out for heat stress.

Yep about a 1' here as well, I start seeing heat stress any closer. That will depend on your cooling though.

eighteen inches for saturation as well as intensity IMHHO

Use the hand test, wherever your hand feels relatively comfortable under the lamp, move it up just 1 inch higher, The lamp not your hand that will give some grow safety space, the best penetration an yeah its one of the most simple and best ways to set lamp height.

what does heat stress look like?