LED Question... please help if you can

Hey guys! Soon-to-be new grower here, I have a question... well lots actually, but only one that this post is about.

I have a 50W tri-band LED from HTG. I'm doing some experimenting with some bag seed right now while I wait for my good seeds to arrive from Attitude. I will be growing in a 15" (D) x 25" (W) x 28" (H) cabinet lined with mylar. Right now I have 4 - 26 watt 6500k CFLs, and I plan on getting splitters for my sockets so I can add 2 more 6500s and 2 2700s (the bulb configuration will be reversed for budding).

That's my basic set up, so back to the question I know that I want to have the lights as close as possible to the plants to get the most benefit from them. From what I have learned so far, about 4" is good for CFLs... right? What is a good minimum distance for the LED? It puts out almost no heat from the area where the lights are, the only heat really produced by it comes from the transformer on the plug. I am going to set up a type of pulley system so I can adjust the height of it as needed, but I need a general idea of how close I can get.

Thanks in advance. This place is awesome! I have learned SO MUCH from here already


** Disclaimer : I am not really doing this, I just think it's fun to role-play like I am. Any and all of my posts should be considered 100% fiction. I am pretending. It is make-believe. **

Edited by Green Phoenix, 05 April 2010 - 09:33 AM.

imo, get a temperature probe and use it to determine distances, no one knows your ventilation, ambient temps, etc.

You can get one that reads only temp at wal-mart for 10 dollars, or a temp+humidity for about 16 dollars at HTG.

Why is this in advanced?

imo, get a temperature probe and use it to determine distances, no one knows your ventilation, ambient temps, etc.

You can get one that reads only temp at wal-mart for 10 dollars, or a temp+humidity for about 16 dollars at HTG.
?

Thanks for the reply, but my question wasn't about ambient temps etc, it was about the distance from lights to plants. As I mentioned in the original post, the led panel throws off almost no heat. Is temperature the only determining factor with respect to the distance between lights and plants? So I can put it right on top of them without any danger?

I already have a digital temp / humidity meter in the cab. As far as ventilation goes, I have 2 120mm pc fans but I have not installed them yet. For now I am leaving the doors open and using a 12" oscillating fan on low from a few feet back... not stealth but I can still unplug the cab and close the doors for a short time if stealth is required. That being said, I'm sure the ventilation is more than adequate for now.

Smoke em if you got em

Edited by Green Phoenix, 05 April 2010 - 10:36 AM.

Thanks for the reply, but my question wasn't about ambient temps etc, it was about the distance from lights to plants. I already have a digital temp / humidity meter in the cab. Also, please assume that ventilation is adequate as that is also unrelated to my question.

geez, just like the real world in here.

Your grow area has specific conditions that we cannot know. There is no magic distance. Get as close as you can and stay under 80 degrees.

Why is this in advanced?

Okay, I wasn't asking for a "magic" number, just hoping there might be a general guideline like there are for other types of lights.

As I said previously, these lights throw off almost no heat, so keeping it under 80 degrees will not be a factor in how close I can get them. If that is the case, am I able to put them within a couple inches of the plants? Should I do this gradually? If they are just seedlings starting out are they still fine to have the light right on top of them or should I have it at a greater distance because they are more delicate at that stage?

Just tryin' to learn.. thanks.

Okay, I wasn't asking for a "magic" number, just hoping there might be a general guideline like there are for other types of lights.

As I said previously, these lights throw off almost no heat, so keeping it under 80 degrees will not be a factor in how close I can get them. If that is the case, am I able to put them within a couple inches of the plants? Should I do this gradually? If they are just seedlings starting out are they still fine to have the light right on top of them or should I have it at a greater distance because they are more delicate at that stage?

Just tryin' to learn.. thanks.

It is my understanding they begin to stress at 80 degrees. Other than that, they cannot have too much light.

That being said. I ran some tests with my 400HPS and I had it down to about an inch with temps stable and below 80. What happened was there was stunted growth towards the center area under the hood. I figure I was at or past the focal point for the hood or something similar. I dont anticipate anyone ever having that issue, as the methods I used to get the temperatures that low were extreme, expensive, and not sustainable, I just wanted to know what would happen.

So as a general rule, get your lights as close as you can and stay under 80 degrees. With good ventilation it is not an issue with CFL's I have found.

It is my understanding they begin to stress at 80 degrees. Other than that, they cannot have too much light.

So as a general rule, get your lights as close as you can and stay under 80 degrees. With good ventilation it is not an issue with CFL's I have found.

Okay, sounds good to me. I'll try lowering the LED to about 4-6" above my seedlings and see how they respond. Thanks for the help.

I've never grown with LED lights but, if heat isn't an issue, I'd get as close as physically possible. With my T5 fixtures, I keep the tubes about two inches from the top of the plants. On my 1000W air cooled lights, provided you have good air flow cooling the bulb, I've actually had some plants try to grow and wrap around the hood.

I'd keep the LED lights an inch off your canopy, as long as you aren't burning anything. The only problem is that you'll constantly be needing to adjust the height as the plants grow up. Under the T5 lights, one or two inches of growth daily is what I'm seeing.

I don't really have a "canopy" just yet. I'm in the seedling stage still. I have raised the LED back up to about 15". I had it at 4-6" for a few hours and watched it closely because I was worried that it would be too strong for the seedlings at that distance. Unfortunately, my concern seems to have been well placed because I began to see browning on the tips and around the edges of the leaves.

It is unlikely that the problem is from heat, because the light gives off very little and the digital thermometer (which is right by the plants) has been at 72-75 the whole time. I haven't had any signs of this previously and the plants haven't been given any ferts recently, so it seems the lights were the cause, right?

I'd welcome anyone who could share some insight on this as I try to figure out my new LED, especially from anyone who has had experience using LEDs. As I mentioned in a previous post, it is a 50 watt, tri-band led panel from HTG.

On the upside, I'm just experimenting with some bagseed till my order arrives from the 'Tude (knock on wood). This is exactly the type of mistake I want to find before I start a real grow with seeds that cost real money.

Hey, I got some seedlings and two mothers under a pair of 90w HO/Blue White LED lamps. Had some problems with the little ones (nute burn stunted growth). But the mamas are loving their light.
I personally love LED lights, will be using more when/if I need em.