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Three K's of florescent lighting

Posted by deweymn z4mn (deweydl@go.com) on
Fri, Mar 9, 07 at 2:30


I am by no means an expert in lighting. I know about and have used different types of florescents like Cool White, Warm White, plant and aquarium, Gro Lites, and full spectrum lights (whatever they are).
With my recent seed starting trays I noticed something. I had a couple of cell packs, about a dozen plants sprouting and they still had the first two leaves on and were about 2" tall. Above them, 3" or so, was a 15" warm white bulb. To the left was a T12 cool white bulb in a smaller fixture. That was going to be a special area with a seperate light timer. Well, these little buggers were bent 90 degrees toward that light that I had left on for a day or so. They favored that bulb over the warm white that was closer.Ok, so I switched them to a new area with the newer sprial 13w bulbs. A strip of six of them and they get more heat from those spirals and seem to be doing fine along with the other seed trays I have on that shelf. The temp seems to hold about 75with the lites on and 65 for the six hours it is off. As you can tell, I am experimenting a bit.
Anyway, back to the three K's.
I stopped at a local big box retailer and looked at their florescent lighting options From what I could find on the bulbs and packages I found that it is confusing for sure. And they don't all have the full info on the package but here is what I found:
K lumens (Don't look that word up in the dictionary unless you have a masters in library science)
Kolor Temp (A K figure listed on most bulbs....Cool white has a higher K than warm whites...plant and aquarium lites have the lower lumen figure but didn't give the K value but I assume it is also lower)
Kost (Varies but seems to rise with pretty packaging/fancy names rather than lumen or K value?)
All the lights that I looked at were GE and that was the main brand that this retailer sold.
F30T12 36" Kitchen and Bath 2200 lumens 3000K $6.96ea
F40T8 48" Kitchen and Bath 2800 lumens 3000K 9.64 2pk
F40T12 48" Daylight 3050 lumens 6500K 9.64 2pk
F40T12 48" Residential lite 3150 lumens 4100K 3.86 2pk
F40T12 48" Ecolux 3050 lumens 6500K 9.64 2pk
F20T12 24" Sunshine Full Spectrum 875 lumens 5000K 6.24ea
F20T12 24" Kitchen and Bath 1275 lumens 3000K 5.97ea
F20T12-KB 24" Kitchen and Bath Ultra ------- ------ 5.97ea

So, what does all this mean? I'm guessing from the above the daylight bulb is what seedlings would get the most from. I'll monitor my spiral bulb plants and have enough trays with the same seeds/potting mixture and do a comparison. And, I stopped by a charity thrift store today and found 6 24" bulbs for $1 ea that are cool whites and two gro lites so to heck with the above retailer. The bulbs looked good/unused but I will test them out. At least they were not black or scarred on the ends so they might be ok.


Follow-Up Postings:

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RE: Three K's of florescent lighting

"k" means thousands, as in thousands of lumens. Sometimes they write is out in full, like 3,300 lumens, but when the numbers get big they might write 10k lumens for ten thousand. Lumens is how much light you have. It really means how bright the light appears to the human eye, not to a plant, but most of the time its all you've got so go with it. With fluorescents, get the most lumens and you won't go far wrong. Too few lumens and plants will stretch,

"K" means temperature, it stands for Kelvin. A Kelvin degree is the same size as the Celsius degree, but 373K = 0C = freezing point. Not helpful if you work in F degrees! All you need to know is that bigger K is "hotter", which is bluer and therefore referred to in lighting as "cooler". LOL! 3000K is warm white, sometimes called soft white, an slightly orange colour designed to be similar to an incandescent or halogen. 4100K is cool white, the traditional colour for fluorescemts. 6500K is often called daylight, it is close to the colour of direct sunlight, in practice it is more blue than direct sunlight. Get cool whites or maybe daylights for plants.

Cost is slightly higher for the most efficient and long-lived fluorescents, often higher for warm whites, sometimes higher for 6500K, and a lot higher for true full spectrum lights. The GE Sunshine is a pretty good full spectrum light, but it is an old design and really quite inefficient by today's standards, not much light and the brightness fades quickly. There is a trend that higher power costs more, but four-foot fluorescent tubes tend to be the cheapest because they are manufactured in bulk.

Dollar store fluorescents are garbage, literally a waste of your money because they will waste more electricity than you saved by buying them. They'll probably also only last half as long as a decent tube. You don't have to spend big bucks but do get something designed in this century ;)


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RE: Three K's of florescent lighting

Why is it when you buy cool white bulb in two different brand names the colors are slightly different from each other ?
They should be the same color?


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RE: Three K's of florescent lighting

If you buy your fluorescent tubes in 10 packs you can save quite a bit, assuming you have need for 10 bulbs. I seem to remember getting a 10 pack of daylight bulbs for around $27 at Home Depot, which comes to $2.70 a bulb, and these were Phillips Altos which are a better bulb than the GEs I looked at (more lumens, longer life, better color rendition index).


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RE: Three K's of florescent lighting

If I remember right, 48" fluorescents are more efficient (give out more light) than 24" ones. Both are quite a bit dimmer toward the ends, so even if they were just as bright you'd get more usable space with longer bulbs.


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