LED light burn; discussion/suggestions?

[69cobrajet]

Greeting all, I was wondering if anyone has any thoughts about light burn with LED fixtures. I've been growing for years with a 600w hps in a 4x5 room with much success and few issues. This year I picked up (2) Vipar Spectra 450 par lights for the same space. I experienced light burn and yellowing leaves for 2 grows now. I've got them dimmed to 50%, increased the distance to the plants as in the instructions (30" currently) and everything else (soil, nutes, water) is the same. My plants still have some light burn and my yield from the first harvest was less than its been with the 600 hps. The plants look like they are nitrogen deficient, yellowing leaves, burnt tips, but theres no way that's the case. Growing in 'super soil' with plenty of compost, homemade worm castings and organic nutes. Anyone else have any thoughts/similar issues/suggestions? I'm thinking of going back to hps or trying out a ceramic metal halide. Thanks to all in advance!

[JohnEmad]

I am not experienced with anything but LED so subbed to see what the more experienced have to say.

[FlyingDutchPaddy]

hi there,

i havent had the same issues you have using LED lights, thus a tale of my experiences with.
what i had was a Budmaster G.O.D. 4 fixture (190W from the wall) for a 4x4 tent, using a recirculating DWC system.

on my last grow using that light, i had 4 white widow xxl auto's.
gemination/seedling stage, i had the light about 5ft from the top of the netpot.
once they were a bit bigger, (5th node of leaves) i dropped the light to about 4ft from the netpots, and left them there throughout the grow.

eventually, once the 4 were fully grown, there was still about 2.5 ft between them and the plants

never did i see an issue with light burn at those distances.

in the beginning, i had an out of control monster plant that grew into the light - that did start showing light burn around 6" from the light.

--

with this new tent i have (5x10ft) ive got 2x 315W ceramic lights.
never before have i seen so many frosty flowers as under these lights.
i have 4 moby dick xxl auto's in week 12 now (frosty), and 4 pineapple express auto's in week 7 (showing white hairs now).

if you're considering going back to HPS, 600W, maybe give thought to the ceramic bulbs.
they are available in 630W double lamp (2x315) / single double ended bulb configuration.
or 2x 315W fixtures.
and the ceramic bulbs give a 'natural' light.

hope that helps.

FDP.

[69cobrajet]

Thanks for the suggestion FDP. Maybe I need to increase the distance. I've heard good things about ceramic bulbs, I'll consider those too.

[Farmall]

69cobrajet first, if your one of those Mustang nuts, my cousin has the same problem... he just sold his 69 fastback with a 429 blah blah something ...but that’s all he talks about.

second, I started with cheaper Chinese leds from amazon totaling 600 watts at the plug and had to keep them about 36” off the canopy but eventually ran out of ceiling height and tips were 6” from the lamps with some light burn. The CMH , a 315 Phillips Bulb, did a marvelous job and just produced some great 10” and 12” colas. I then upgraded to some full spectrum Samsung 301b strips and have found a great compromise in electrical efficiency and flower growth. These leds are super bright but I have found that 16-18 inches is plenty of space over the canopy as the plants get stronger and taller....the drivers are mounted outside the grow area so heat is minimal and the strips themselves produce very little heat averaging 77F in summer ambient air....in my opinion....the CMH is my choice over high end led’s based on acquisition costs and darn good bud production. Although I love the LED’s. I do need to do a side by side comparison using clones to really see what the biggest differences might be.

i did find with D.A.A.S.69 guidance, that several 100w 6500k cfls get seedlings off to a very solid start...full, thick, squat and exceptional green color. After 2-3 weeks, they would go to the LED’s

[dphipps1020]

LEDs you have to use the manufacturers specs. For example, I have a 1200W LED (130 actual) in each of my 4x4' tents and the lights are maybe close to 30" above my canopy and I have no issues with mine. I'm also running an 8x8' with 3 of those on one side and an HPS set at 750W on the other. 8x8 tent is flowering and going good so far and it's recommended closer for flowering so I have those right around 20" I think. Not sure what else to suggest except keep the specs handy and try to follow them.

[homegrown]

Hey 69cobrajet, what kind of airflow do you have? Do you have fans blowing across top of plants?

[69cobrajet]

Good question Homegrown, I've got an 8" oscillating fan in there. Its not a big breeze but it doesn't feel too warm.

[JohnEmad]

There is such a thing as wind burn if the breeze is too strong and blowing directly at the plants I believe, although I haven't had that happen yet...

[homegrown]

That is odd 69cobrajet , Im running 2 600 viperspectra in nearly the same size tent, and running lights much closer than recommended specs and have not had a burn issue. My firs grow i kept the lights at around 18-22". For my current grow im running these lights at 14-16" above the canopy to test bud growth difference. Still no burning......i do have an oscillating fand blowing across plants and another fan blowing air through the plants. Are you venting air out of the tent?

[SoOrbudgal]

Very true JohnEmad the plant drys out quicker as if it were out doors 85 degree days windy

[Mrblu]

I use viparspectra v450 and no issues, I have even subtracted 2 inches from the suggested hight. Could your lenses be smudged or scratched creating a hot spot?

[69cobrajet]

Hey it sure is odd. Everything else is the same except for the lights. MrBlu's suggeston of a problem with the lights being somehow defective is something I've been thinking. They're in a small room (not a tent) built for growing (back in the days of 'prohibition') so there's steady ventilation. Right now the lights are 30" above the tops and dimmed to just under 50%. If I kick them up a bit I'll get that leaf yellowing shortly after. I might just pop the 600 hps back in just to prove to myself that it's not something else. A big thanks to all who responded! And Farmall, yes, I was bitten by a cobra years ago and now have a tendency to obsess about Mustangs, unless I'm very stoned
69CJ

[Farmall]

I know it’s fun... I even know stuff like Q code engine and ‘rustangs’ as he called it. He has restored a 1970 convertible with that 351 Q code in the vin. It was so sweet, sold it for some house somewhere he wanted to buy ( probably his wife). 😉

[pacodelahoya]

The led's aren't giving you the same evaporation rate that your previous light did so the roots aren't sucking up everything out of the soil at the same rate they once did. Even though you're feeding the same levels, the plant isn't taking it up at the same rate. The plant is getting enough light to grow but what does grow isn't getting the same nutrition level under led as it with hps, hence the signs of deficiencies. I had this explained to me by a successful grower and his advice was to raise the temperature in the grow area by a few degrees as it will cause the plant to transpire more. I saw positive results in less than 2 days. Might be worth looking into.

[69cobrajet]

Thanks, thats easy enough to try.

[Sledrock]

I use viparspectra v450 and no issues, I have even subtracted 2 inches from the suggested hight. Could your lenses be smudged or scratched creating a hot spot?

I have a Vipar 450w also and haven't had any issues. I was keeping my light at 21" but it's now at 19" due to plant (White Widow) getting taller. I'm going to leave it there and see how it responds, might lower even more an inch at a time.