I’m on my fourth successful grow and use CFLs, 300 watt LED , and 600 watt HPS. I’m particularly looking to hear of others experiences with LED lights. What is the closest anyone has used them without burning ?
I had my mars about 8 inches away. It toasted some leaves the buds went nuts. My dr grinspoon likes the light farther away, about 20" same light on bloom. I play around with mine and during beginning flower I keep light further away, more stretch with LEDs.
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@Givemefire I can’t believe it somebody else that likes stretchy plants. I can’t believe it.
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It really depends on the par values of the light. There is too big of range in light output for a one size fits all measurement.
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Yes but is for safety major. You can lower or higher your light starting from that chart
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Yep, unless it’s a weak light and then being safe would be wasteful.
You want to target 600-1000 ųmols at your canopy during flower. Less will sacrifice yeild, more will need co2 supplement. It’s considerably less during the veg stage, and even less for seedlings.
A light that produces 600 ųmols dead center at 12" you could expect it to be just enough light ran at 30" for seedlings. If a different light produced 2000 ųmols at 12", 30" probably would be pushing the seedlings. So going higher or moving the pots to the side would probably be needed. That same light would probably burn any buds directly underneath it flowering at 12". The light that produced 600 ųmols at 12" would be great at that height for flowering. But that light ran at 20" or more for flowering would cause a lot of stretch and fluffy buds.
So light output is key when determining operating height for any light.
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Based on my little cheapo light/moisture/pH meter, mine have close to 2000 at the cola. I never checked because they looked healthy, but you got me curious. So, for what it’s worth I noticed a slight yellowing of the fan leaves that I saw as a nitrogen deficiency (Co2 maybe?) so I added a layer of used coffee grounds to each pot. The next day everything greened up and they are still n getting the 2000 juice.
But for random reasons my plants are over 160 days old in week 5 flowering, so they may just have a better resistance. The stems look more like trunks, I may whittle them into a pipe 
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I can’t really attest to methods of supplementing co2, nutrients, or deficiencies. But if you’re hitting your plants with 2000 ųmols I would expect to have to have to supplement at least co2.
You may not see any bleaching or burn so to say, but you’ll definitely be wasting your light at anything over 1200 ųmols. I would consider raising your light a little and sharing the love to the rest of your plant.
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@dbrn32 I’ll give it a shot. It is about 15"-17" above the cola, and that doesn’t seem too close for a 300w while they are in flower. I have carabiners that are about 2" long holding up the light. I’ll remove one (raise 2") and see what happens. It is noon here, and my lights will go out at 7pm-ish. I’ll take a before and after and see. Can’t hurt!
Also, I don’t have a lot of faith in the meter. 7.99 at the hardware store. I use it mainly for moisture.
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Is it 300 wall watts? The 300 watt models I’m familiar with draw about 100 watts and typically provide 300-500 ųmols at 12-18". Not to say yours doesn’t, but 2000 ųmols from a light you referred to as a “cheapy” seems suspect. Is there a chance you’re measuring something different than par?
Its a MarsHydro 300w Full Spectrum yada yada… Cheapo compared to some I’ve seen. $69
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No problem with your light. Amazon listing says 760 par at 12" and 493 at 18". I severely doubt they under advertised that much. So I’m not sure what you’re reading, luminous Flux maybe?
$7.99 seems really cheap for a par meter too. Even the cheaper ones I’ve seen are like $100 and up.
Definitely not picking on your light or meter any either. I just don’t want to give you bad information. The 2000 ųmols seemed like a lot to me is all.
Some of the yellowish tint is from the LED’s, but you can see a difference between fan and sugar. Hell, it might be a strain that is supposed to be like that. Bag seeds. Meter pictured. I think it measures lumens
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That’s just the top - check this out:
Feedin the bitches good this week, they gonna get McDonalds fat!!!
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I would disregard what I said about the light height then and treat any deficiency as nute/ph/water issue as you see applies. I don’t think you’ll get any light burn at +/- 12-18" with that light at your current stage.
Also, you can maybe use the meter to compare some stuff, but measuring lumens on a blurple light won’t tell you much. They aren’t designed to look bright to humans (lumens), but to be high in photosynthetic radiation.
Plants look good too!
I have no clue what the meter measures, but it DOES measure basic brightness effectively Thanks for the height advice! I had been crowding the girls together to get them under the light best. Now I am taking full advantage of my “make it sexy from underneath” light on the side 
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If you’re concerned, you can Google lumens vs par and get a way better understanding than I can give you. But we would only really consider amount of lumens as far as plants go when discussing the same type of light and spectrum. More lumens of the same spectrum should create more par. Just because something looks bright doesn’t mean it has a high amount of par, and ■■■■ versa.