How much of a fan is needed for seedlings? New lamp setup (pics)

somegeek(8b Wash)March 31, 2009

My wife and I took a crack at starting plants from seed last year and had minimal success. Dampening off and lack of sunlight were the main culprits. This year, I'm determined to get those good looking starters I keep seeing on this board, so I put together a grow light lit area. Single ballast with two 4100k 20Watt T12 Sylvania bulbs and a custom build coroplast hood(I still need to spray the inside with flat white). Lamp is hung crooked due to differing heights with starter containers:

How much of a fan / breeze do you require to stimluate the seedlings to grow sturdier as they shoot upwards? I have a low speed 80mm PC case fan powered with a wall wart which puts out a mild breeze. Also - does this dry out the surface quicker?

Appreciate any input.


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I use 4' cool white 40 watt fluoro's and have good success, now I am not sure what the diff. will be using 20 watt bulbs. I think you will need a larger fan when the seedlings get bigger but for now that one should be good enough. I do not even use my fan until plants get about 3" tall and use it for about 15 minutes three times a day.(it's on a timer)Setup looks good. And yes, a fan will definetely dry out the soil faster.


    Bookmark   March 31, 2009 at 3:24PM
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somegeek(8b Wash)

Thanks for the reply. These 2ft bulbs are rated for 1200 lumens each. Not sure what youre 4ft bulbs are putting out?

I do need to pick up a grounded timer for my light. Good idea to put the fan on one as well!


    Bookmark   March 31, 2009 at 3:42PM
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The standard 4 ft 40w flourescents I have put out 3100 lumens each. I rigged up a 2-shelf rack out of 2x2's and have two fixtures per shelf (4 tubes/shelf). This is my first year of starting seeds (actually first garden PERIOD), and I'm just learning as I go here, but 1200 lumens sounds a bit low to me.

    Bookmark   March 31, 2009 at 4:18PM
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I'm thinking that it's a bit iffy with the 2' T-12 lights too... at 1200 Lumens each (2400 total). It's probably just barely enough light with the plants almost touching the tubes. For less $$$, using the same hood that you got there, I'd take a piece of wood and bolt in 3 or 4 regular light sockets and intall CFL bulbs. Assuming you use 13W CFL, you'll get about 4x800=3200 Lumens and if you used 25W CFL's you get about 4x1100=4400 Lumens. Note that the actual lumens will depend on the brand of bulb that's available in your area, but it won't be too far off.

However, since it's already setup, please keep us posted on how well it does. Also, do you know what kind of ballast is in that light of yours? If it's digital, and you are willing to tinker with it, you might be able to overdrive it to give you about 50% more light.

    Bookmark   April 1, 2009 at 3:13PM
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somegeek(8b Wash)

1200 per bulb not being enough kinda threw me off when you compare this to the lumen output of the T12 'grow lights' being under 1000 lumens but I'm new at this so that idea is relative. :) The CFL idea is intriguing if this setup doesn't do the trick since my local big box store has standalone sockets for $1.45.

How can I tell if my ballast is digital? I did take a look at it last night to verify it's max power output and with the 20W T12s, I am at the max where I am now.


    Bookmark   April 1, 2009 at 3:39PM
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Lumens is a measurement that's biased toward the human eye, not plants. Most of the light used by plants don't appear bright to our eyes, so the flouro grow lights will always have less lumens. Personally, I've used both and didn't find too much difference between the grow lights and the regular cool or warm whites.

I forgot to answer your original question... easiest way to tell if your fan is enough is to check to see if it visiblly moves the seedlings. You just want to shake them around slghtly to encourage them to grow stronger. If they arn't moving in the breeze at all, than you either need to put the fan closer or get a bigger fan. I use an osscilating fan myself, and it's hooked up to the same timer as my lights.

As for your ballast, short of opening up the light and check, if it hums a bit when it's on, it's a magnetic ballast. Also electronic ballasts are very light weight while the older magnetic ones are quite heavy. Otherwise, you'll have to open it up and look inside. Usually, if it's an electronic ballast, it'll say on the label.

    Bookmark   April 2, 2009 at 9:16AM
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somegeek(8b Wash)

My Dahlias are popping up and don't look leggy like other starters I've had in the past. These were planted seven days ago and I put the light over them about four days ago.

My first Lettuce Leaf Basil starter...

Soil is a bit moist as I just shot a few spots of mold with Chamomile tea as well as the shoot... otherwise I've been letting the surface dry up.


    Bookmark   April 2, 2009 at 2:56PM
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