How far from light source..?

I have a 400watt in a 7ft tall by and about 2 ft wide.. the plants are on the floor now, i only have two at the moment, just got em yesterday! but ive have issues with clones in the past, so i was wondering if they where just too far away from the light. any suggestions?

If they are clones they wont want much light unless they are rooted. I would say stay 18-22 inches away and move it closer as they root.

If they are established plants see the attached chart to judge distance. Keep heat issues in mind when choosing a distance though.

thanks for the chart man. i just got them yesterday so they arent rooted in the soil yet, but the guy i got it from said theres crazy amount of roots in the rockwool that their in.. im gonna try putting it a bit closer to the light, according to the chart