It's hard to say specifically. I use ViparSpectra lights, too. They have recommendations that are a good place to start. Something I do is start low and gradually increase the intensity until I see signs of light stress. When I see it, I reduce the power or increase the distance from the light to the plant's crown. Young plants can't take high power, so 25% might be a good place to start. That's about what I use for the little ones.
It's hard to say specifically. I use ViparSpectra lights, too. They have recommendations that are a good place to start. Something I do is start low and gradually increase the intensity until I see signs of light stress. When I see it, I reduce the power or increase the distance from the light to the plant's crown. Young plants can't take high power, so 25% might be a good place to start. That's about what I use for the little ones.
I use my XS1000 in a 2x2x3 tent for seedlings and early vegetation. 18 inches is about as close as I let the plants get to the light. I've had some trouble with light stress or burn.