PPFD (the spectrum of light that the plants see) is relevant here. Though PPFD might not mean anything to you, the relative comparison for the various growth stages are useful:
Seedling stage: 300 PPFD
Veg stage: 600 PPFD
Flowering stage: 800 PPFD
Some MH growers will probably come along and help, but in the meantime the most important rule is to not expose your young plants to heat from the light. If you can feel heat on the back of your hand when it is held plant high, then the light is too close.
I let the plant tell me how much light she wants when young. If nodes are spaced too far apart, then the light is too far away. If the nodes are spaced too closely, then the plant is getting too much light.