[Jellyfish]

I switched from CFL's to LED lights not too long ago. My first run with LED's went fine, but on the next two, I kept lowering and lowering the lights, to get them as close to the tops as possible.

By the time I got to the third run, my fan leaves were yellowing and falling off. By the end of that run, there were no fan leaves left.

I just would not believe that the problem could be too much light, because my temps were fine, yes, even at the top of the canopy.

I had to end that run a little early because without fan leaves, there was no more growth.

AFTER that run, I did some research and discovered that, YES, it IS POSSIBLE to give your plants TOO MUCH LIGHT. Even when the temps are down.

So this run, I have the light 18 inches over the canopy like the manufacturer suggests. And things are going much better.

I'm posting this in case somebody might have a similar problem.

This article explains everything- PSA: Too Much Light?*****
*****Okay, as Ronin4life pointed out in post #2, the link doesn't work. But you CAN use your favorite search engine to find it, searching under "PSA: Too Much Light?" The article is on a website called grow weed easy dot com. Thanks to Ronin4life

[Ronin4life]

Thanks for info...the link consent work for me.

[growingcrazy]

I am just going to toss this out...

This summer I did some testing with vegetable seedlings that were started indoors under hps...

I wanted to see the results of putting 2 groups of plants outside, one hardened off as usual, the other directly into sunlight. I divided the full sun group into 2 groups also, one that was left alone as control and one that got magnesium foliar sprays.

End result was that the plants that got the foliar had very little issue with going to direct sun, the other half struggled and started to show def. before they came back around.

Not conclusive but it satisfied my hunch.

Long story short...You can feed to match the light intake if all other parameters (temp/humidity/moisture) are met. Within reason of course...

EDIT: I am not sure who did the PSA test, but you can see that the plants have similar def. each time... This isn't the plant or the light in this instance, just the grower. Increasing EC doesn't mean the plant is up-taking what it is in need of.

[repuk]

It can, definitely. Just had to replace a previous HML I built for a previous grow on a different space; when used on a veg tent (garden shed grow in my sig) my plants cooked... so I'm replacing it with fluorescents.

Veg tent height is 60cm/23", running a string of 10 XM-L's (at 90W total) cooked the plants leaves, I raised it and even at full height it's clear the plants are not digging it. It will be a different story if LED chips were 3W (XM-L's are 10W), so individual LED power has to be taken into account also, not overall power only.

I'll be using 110W for the fluorescents and from previous grows I'm positive I can lower them until they almost touch the canopy and all leaves be perky and happy.

[Jellyfish]

I agree- with fluorescents, you don't have to worry about too much light or heat.

[StevenJennings]

Yeah man. I was noticing tht some of my canopys nugs were smaller than the othere but were closer to the light. Bumped em up a few inchs and they started to fill and maintain growth. Dont let em go too long or you can bleach your nugs and ive heard tht it takes taste and potency away from nug. Not from experience. Just read it somewhere. Prob on here. Lol. I let my canopy have 18-24 inch from my cobs and they flourish. Too much light is a thing. I never experiemced this until using led as well.

[Jellyfish]

Originally Posted by StevenJennings

I never experiemced this until using led as well.

Right, because they don't give off much heat, they fool you. For my TWO ViparSpectra 450's, 18 inches is the MINIMUM I can have the lights close to the plant tops. Thanks for your comment, StevenJennings!