if your bulb dosn't create heat you would press the plants against the bulb.

what hurts the plants is the heat, we call it heat stress

it is unlikly that you could give you plants too much light.


the difference between 2 and 3 feet is significant
light intensity decreases at a square. ie double the distance you get 1/4 the light

i'd say a 400w mh would light a 3ftx3ft space alright
it dosn't matter how many plants it's the area. you could fit 30 very small plants and they would do fine under it