Micromoles/meter sq. and PAR/meter sq would be lovely but you aren't going to get the data so you might as well forget them. Where the data actually is published, it is not standardised, not reliable, and really little more than a marketing gimic. Lumens are less than perfect but really the only practical measurement you will have. Even some lumen claims are exaggerated but the values are fairly easy to check and data from the main brands is reliable. Given that most fluorescent tubes produce about the same lumens/W, give or take 20%, even watts/ft sq is adequate. Low power CFLs tend to be at or below the lower range of lumens/W so don't skimp on the power. Which CFL do you have? 1700 lumens is typically the output of the 26W bulbs. Do you have a 2/4 pin type rather than one of the self-ballasted ones?

So your first question should be how much light do your seedlings need. I don't know, but I'm guessing more or less full sun would be good? That means you should be looking in the range of 3,000-5,000 lumens/ft sq, which isn't as intense as full sun but the lights will be at full intensity for the whole day and probably longer than a typical summer day. That equates to about 40W/ft sq with good fluorescent tubes, or 60W/ft sq with small CFLs, provided you have a good reflector arrangement to focus most of the lighto onto the seedlings.

OOoops brain slip I have 26 watts 6500k. The seedlings are suggested to be grown in filtered sunlight(light shade)I think. I thought I read that equator @ high noon is 10,000 lumens/sq.ft.? What would that put the midwest at?

Thanks for your help shrubs :*)

Ok another question that is probably asked a lot...
Is a 3000k MH better than a lower Lumen 6500k CFL? The MH seem to be more lumen/watt than the CFL.

Good day

Yes, noon direct sun is generally taken to be 10,000 foot-candles, and close enough to that anywhere in summer. You will not achieve that with fluorescent lighting and don't need to. Sunlight in the morning and evening is not so intense and what your artificial light provides is like morning sun for a straight 16 hours. It works, trust me :)

Are you talking about low power metal halide bulbs like 26W or 50W? They are actually less efficient even than a CFL. Metal Halide lamps don't reach high efficiencies until about 400W or more. Even at their best, modern fluorescent tubes are about equally efficient, so metal halides are really restricted to very large scale applications requiring very high light intensity or very large coverage.

Given the "light shade" definition, I think you should aim for 1,000fc to start out, maybe 2,000fc for growing on larger seedlings. That would be about 20W/sq ft going up to as much as 40W/sq ft with CFLs, a little less with larger more efficient fluorescents. Once you have the plants growing it becomes very easy to judge whether you have sufficient light.

Thank you so much :*) Is 1000bulbs.com or someone else a reputable dealer? Good price/quality? I may get a 85 watt CFL to start.

Good day

I suppose if you just have one pot of seedlings then a cfl might be the best way to go ... but if you have something with more surface area, such as a tray of seedlings, then I would use an overdriven shop light or two. Have you read the thread on them here?

I just got my light set up for this winter and it floods a seed tray with light from all angles ... I took two 4' shop lights and cut them down to 3' and hung them side by side ... I am ready to grow!

Interesting. So I am assuming you mean you cut down the reflector and ballast so you could fit 3' lights? Do you have a link to the thread or a name for it? My area is very small, just over 3' wide, but I do have 3 seed trays to light.

Thank you

That's kind of like my situation ... I want to grow a seed tray or two indoors this winter in a 3' wide area. Based on what I've read here, I bought a couple of 4' shop lights with electronic ballasts at Lowes and shortened them to 3'.

Check about 25 or 30 topics down here ... the thread titled "I have found the BEST cheap flourescent ballast/fixture - cont'd". Most of the thread is about making the 4' fixtures brighter, but what I did was cut a foot off the reflector and create a 3' shop light. It lights up one seed tray with light to spare, and if I want to grow two trays I can swap them out every 12 hours.

I don't believe that a CFL would do as well. I think it would probably light up the middle of one tray.

I posted a picture of my new lights on the test forum. You can see how a seed tray would be all lit up! It was only a week ago that I built them. I used a dremel tool with a cutoff wheel.

Here is a link that might be useful: picture of light on test gallery ...

Results of driving a 3' tube with a ballast for a 4' tube will vary. In the worst case it may not work at all.

If you have a space shorter than 4', I would strongly recommend the 96W compact fluorescents which are 36" long (also shorter forms in lower powers). You are unlikely to get better results by reverse-engineering from a shoplight. Unfortunately, many suppliers are hydro or aquarium stores that choose to market this as a premium product with a premium price. If you have the skills to consider cutting down or overdriving a shoplight you probably have the skills to source a 96W ballast and stick it in some kind of reflector.

I once bought a kit like that from ahsupply.com ... two 96w cfl lamps and a ballast and reflectors. It's real bright but the thing is, the kit and two bulbs cost over $180, and when the bulbs burn out it costs $60 to replace them. I also have a 100 watt metal halide grow light but, again, it was expensive and the bulbs are expensive (and the mh light has such a "hot spot" and doesn't light a tray evenly).

I went to Lowes a couple of weeks ago and they had standard 3' fluorescent bulbs marked down to fifty cents, so what was I to do? I had read here that some shop light electronic ballasts would drive a 3' lamp, even a 2' lamp, so I bought a couple of shop lights and I tried it and it works. I spent about $40 total, and replacement bulbs are affordable (probably won't find any more for fifty cents though).

BTW, have you looked at grow lights on eBay? I've seen some pretty nice fluorescents there, cfl and overdriven t12 and t8 ... but it's hard to find a 3' fixture, most are 2' or 4'.

Here is a link that might be useful: 96 watt cfl kit