400w light penetration?

Gooing to probably be running a bare bulb 400w vert grow in around a 3'x3'x3-4' box with around 4 plants.
I could probably get the lights 4-6" with the right amount of crazy airflow..

So, how far into the plants will the light get?

Cheers!

roughly 20 - 30 inches

400w can penetrate 4 feet at max depending on the bulb,all my plants are less than 2ft tall and each 1/2-2 inches way from bulb,but i'm not in a closed space and i have a tower fan blowing directly in the middle of the canopy where the light is and they are getting good light,although
i do have some light bleaching.when my ladies were in the closet 4ft seemed to be where the light started to greatly diminish.

Wow, okay... that means light should bounce back from the wall, I wonder how much PAR/Lumens are left at that point though.

Oh and is anyone running/have any experience in UV-B lighting? If so, what wattage/proximity are you at with your set up..

Thanks!