300w grow light

Its hard to determine but you should be safe at 60 cm. LED's vary in how bright they are. You would have to let us know what brand/model you are referring to. Is it 300 true watts( pulls 300w from the wall). Is it a cob light or burple ( blue/purple ) light, quantum board. Just a warning, I would not have more then one plant in the same pot at a time. The will compete and bring each other down. A lot of energy will be wasted fighting for root space and light. I would either separate them or select the strongest and kill off the weaker one.

Anywhere between 30cm and 60cm to be safe you can experiment though a hanging guide should of been with the light though there are more guides online you can follow. I think bar lights can go alot lower but i think thats a different story it all goes on what you light you have if the diodes are really powerful even a 300 whatt can harm a seedling I know first hand my telos 0010 pro cannot grow seedlings at a low hang height the 2.5 umol leds are just too bright and that unit is only 285 whatts i think you just gottta experiment yourself :)