Distance light and incorpare hps/mh

Hi, don't you have the indication from your manufacturer? My Marshydro TS1000 is 150 W and for plants very similar to yours, it's about 55-60cm from canopy and looks good. I wont go to 20 cm. Also, the LED lights are not comparable from power consumption. The key factor to compare is the quantity of light (PPF) and how the light is 'spreaded' at a certain height (PPFD). Full ripe plants can withstand as much as 900 umol/m^2/s, but I guess that's too much for a seedling as your. Maybe you can try there if your model is cited https://420expertguide.com/grow-light/cannabis-grow-light-height/. As for the second question, probably you would have to hang the HPS lamp way higher than the LED lamp, especially for a seedling. However I think that during late veg/flowering it could be beneficial, I don't see any conflict if the height is appropriate Good growing!