Seedling Light - When to Change

How long before seedlings from seed, in 16oz cups, should be transferred from CFL to say, a 600 watt MH? The concern is burning up the seedlings under the higher intensity light.

you cant overdose the plant on light.....A cooltube is IDEAL....but I would just say....do the hand test...if it isnt too hot holding ur hand there for a minute, it should be cool enough

I go pretty slow even with a 400W. After I plant the seed I give them a week of CFLs. From weeks 2-3, I turn on the 400W, but I keep it as far away as possible - about 2.5 feet for me. About week 3 I get serious and move that light right in and we get busy.

Assuming you are talking about intensity and not heat.

picasso.....can they OD on light?

Dalamar said:

picasso.....can they OD on light?

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If you take heat 100% out of the equation?

Short answer is that I don't definitively know. I've been told you can't do it simply because even a 1000W light is less intense than the sun, but my experience has been that you can shock them with a rapid change.

It's also important to remember that light intensity increases by a squared factor of distance. So if you move your light half way towards the plant, the intensity isn't 2x greater, it is actually 4x greater. Move it 1/2 closer again and intensity is now 16x greater.

Hope that helps.

ok let's get this debate settled. We know for certain that excessive heat is dangerous to young seedlings, but how about the intensity of the light itself?

DRCANNABIS said:

ok let's get this debate settled. We know for certain that excessive heat is dangerous to young seedlings, but how about the intensity of the light itself?

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It will be great if someone knows, but my experience is that it really doesn't matter. Light is light for young plants - after a certain point it is just wasting light. Where the bigger lights really shine is reaching lower leaves in a big canopy of plants.

I wouldn't spend much time worrying about this. Get some light, any light, on seedlings and all is good, you aren't going to lose any productivity.

I just put them right into bigger pots and directly under the 400w HPS for 12/12 but never close enough to get too hot. A buddy of mine went from CFL into his 400w flowering chamber and repotted into bigger pots all at once, but he gave them a week of 18/6 under the 400w then graduated down to 12/12 over a few days. His harvest was huge and I think that extra veg time under the 400w and in a bigger pots really helped.