DE 315W CMH: Height & Dimming

[Veritas629]

I've recently started a new grow, only my second actually. I've also got a new light, HiPar DE 315W CMH (double ended bulb, not two 315W bulbs) with control ballast (dimmable 50-100%). My only previous light was a HLG QB, so this is new tech for me. Tent is 60*120*210cm and has three seedlings in 4L organic soil pots. It's my understanding that CMH works well at 30-60cm over the canopy. But what advice would you fellas offer for seedlings? Plants have their cotyledon leaves and first set of proper leaves starting. They are a little tall and floppy, maybe from too long in the dark before potting them. The light was at the top and 50% dimmed, because I didn't wanna fry the babies. Today I lowered the light to about 90cm over them, but still 50%. Is there a guideline for when I should lower more and/or turn up the light power?

[fred_hawk]

i got the same light but not putting them under it till the second set of leaves

[Carbcon]

Never had a dimmer.

 

315 not a super hot light, I never had any problems with seedlings.

 

I'd be full power and play with the height for temps.

[ZEN2U]

I'm using a Dual 315W CMH unit. Unit does not have a dimmer.

 

My lights are set up for the moment at 750mm above the babies and have been since they broke ground. They have their 4th set of true leaves coming out strong(will be topping them in a few days). No signs of leaf burn or heat stress in the 4 plants. I can feel sweet FA heat at plant tops. At flower time the light is 600mm above SCROG.

 

Mind you, I have 2 fixed 6" fans blowing(24/7) across the plant tops and there is also a fan pushing and pulling(24/7) 420CFM of air in the 1.2 X 1.2 X 1.8M tent. The whole thing runs that cool I had to put 4X aquarium heaters in the DWC buckets to keep the nute solution at constant 18C.

 

Sounds like your light is too far away and too dim.

[Veritas629]

Thanks for the advice. Earlier today I lowered to about 70cm above the plants and bumped up to 60%. I'll bump it up 10% a day to full power. A bit of a ramp up to avoid shocking the wee lassies....

[ZEN2U]

All good, as long as you have sufficient air flow and everything is cool(your light produces less heat than mine) inside your tent, you should be fine.

 

When the babies get a bit larger, you can consider dropping the light to 600mm and observe for a few days for adverse effects. If it works out fine, then rock and roll.