New grower - LED light tips please

[Canuckbuds]

Hey everyone, first time posting and I have a lighting question. I'm an electrician and managed to salvage some LED lamps from a job I was on. They replace 400w MH lamps and draw 165w. My seedlings seem to be growing quite slow and I'm wondering if these lights don't put out the right light spectrum for plants.

They're the EX39 lamps on the second page if someone could provide input. I can convert back to MH lamps if I have to, was just trying to save in power consumption. Once the plants are bigger and going to convert one to a HPS.

 

[Scientific]

I took a look. No reason those shouldn't work fine spectrum-wise. At 20,000 lumens each, if their light was spread out over one square meter (about 11 square feet) you'd need three of them to give you 60,000 lux for good flowering.

 

[Canuckbuds]

Thanks. I have two of them in an area about 8x7 feet. I can raise and lower the lights/plants accordingly. I'm on the lookout for more fixtures I can recover from work to make additional light.

 

[Scientific]

So doing the additional arithmetic, your 56 square foot area is about 5 square meters, so with two, 20,000 lumen lamps, you have 40,000 lumens spread over 5 square meters, so you have 8,000 lux. You need at least five times that much for good vegetative growth. To answer your original question, that deficit would definitely cause slow growth. I would expect the plants to be spindly as well at 8,000 lux.

I envy you being able to get free lights, and those lights are good for 50,000 hours! You just need eight more of them to get a good vegetative illumination level (40,000 lux) for your big grow area and 13 more for good flowering illumination (60,000 lux).

 

[Canuckbuds]

Lol they are $220 a piece to buy just the lamp. It's so bright in the room you can't even look up without it hurting your eyes. Looks like I'll be moving the plants outside if I need that much more. Would I be wrong in saying that if I raise or lower the plants or lights to be closer I would be increasing the intensity of the light in the plant. I have the seedlings sitting about a foot from one lamp right now.

 

[Scientific]

Even an array of four 1600 lumen lamps hurts my eyes. I'd love to see a 20,000 lumen!

Those light calculations are based on the lamps evenly illuminating a flat surface. When you bring the lamp closer to that surface, the light intensity goes up exponentially, so twice as close is 4 times as bright, three times as close is 9 times as bright, etc. For all of my doom and gloom about not having enough light, if you have a 20,000 lumen light just a foot away from seedlings, it could even be too much light. A $16 lux meter is something that seems unnecessary until you have one, then you use it all the time to optimize light placement. I use the one in the link all the time.

 

[Scientific]

Looks like I'll be moving the plants outside if I need that much more.

Noonday sun on a clear day is 60,000 to 100,000 lux for free. After I got the electric bill for my last grow, those free photons are looking really enticing (if the sun ever comes out here...)