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newbie confused on T5 specs

Posted by wendyb 5A/MA (My Page) on
Thu, Dec 6, 07 at 15:57

I have to replace a T5 bulb that is 24 watts, 6400 Kelvins, 2800 lumens.

I found one that is different wattage. I have found different kelvins (3000 and 4100). I found one that said "high output". My original one didn't say that. So far I haven't nailed down the lumens for these potential replacements.

My question is basically compatibility with the existing fixture...are any of these specs tied to the fixture in use?

I know that Kelvins affect the growth charactistics...color spectrum. I want 6400 for daylight. But what about the other specs? will they work in my existing fixture? Originally my fixture came with the bulbs that I can't find exact replacements for.


Follow-Up Postings:

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RE: newbie confused on T5 specs

The 24W T5 bulb (approx 24" I assume?) is a high output tube whether it said so on the label or not. You can replace it with a 24W T5 high output (HO) tube.

You can use any colour temperature you like that has these specs, but you probably want one that matches the colour of your existing tube. They are available in 830 (3000K), 835 (3500K), 841 (4100K), 850 (5000K), and 865 (6500K), in ascending order of blue-ness, descending order of orange-ness. I haven't seen 6400K tubes but the 6500K would be indistinguishable.

Don't try to use a tube with a different wattage, it may not work.


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RE: newbie confused on T5 specs (lumens)

I've just checked the specs for 24W T5 tubes and they shouldn't produce 2,800 lumens, but 2,000 lumens.


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RE: newbie confused on T5 specs

ok, that helps. Thx

the original one says it was 2800 lumens and 6400 kelvins. Yes it was 24" (metric). Maybe they are bad specs. Here's the link, but its no longer available.

discontinued item at gardeners supply

I will try again to look for 6500K 24" 24W. Maybe my search for 6400K took a detour.


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RE: newbie confused on T5 specs

That one says 2280 lumens which is more believable.

This place seems to offer the exact same 6400K 2280 lumen tube. You really couldn't tell the difference from a 6500K tube if those are easier for you to find.


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RE: newbie confused on T5 specs

The Sun is at about 5500K, and 4000K is often referred to as full spectrum. Fluorescents can NEVER replicate Sunlight in any meaningful fashion. They are linear, and have no amplitude(meaning they have no intensity). They're filled with mercury, another negative. They also heat up and glow, instead of burn and produce plasma like the Sun or HID. Don't waste your time with fluorescents. They're a joke.


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RE: guess the joke's on me.

Well, I'll tell my greenhouse that the fluorescents are a joke. My tomatoes, brocolli, peppers, twenty-five plus types of herbs, flowers, lettuce, spinach and the like will probably keel over and die then. Up until that point, however, they have grown and thrived so well; I'll cry quarts, I suspect.

My greenhouse is a huge success with only FL lights and the poor suinlight from a western PA sky. It is nine degrees out and six inches of snow on the ground. Inside my greenhouse, though, it is summer. My coal furnace (free from craigslist) keeps it a toast 70 degrees all the time.

FL are far from a joke; they are cheap, efficient and do a wonderful job. Now, if you need to grow some doobie-weed or other high maintenence item, maybe not.

Now, this is just a poor greenhouse owner's opinion. I'm no high-faloouting expert or anything. But, if I'm being truthsome, FL lights make winter bearable.


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RE: newbie confused on T5 specs

SnB you found it!!! Great job! that *IS* the bulb. Thank you thank you thank you


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RE: newbie confused on T5 specs

Plant growth is largely a function of how many photons are incident on the plant, but the cholorophyll activity is highest in the red zone. For that reason I use 3000K lamps for all of my growing. 6500K will work, but it just doesn't have as much red as a 3000K lamp. I searched all over the internet for studies on which fluorescent is the best, and you will find that almost all studies recommend warm white only (3000K). Some growers use cool white 4100K.
The designation of "sunlight" fluorescent is only a reflection of the degrees K rating of the lamp, but study the published line spectral output by the manufacturer, compare it to the PAR curves of plant growth, and you will see the theoretical basis for using 3000K lamps, which matches with what happens in practice.
Someone actually published pictures of plants grown with each different type of lamp, and compared them with natural sunlight and the Kitchen and Bath lamp (3000K) was the clear winner, and was better that natural sunlight. 6500K is very popular with cannabis growers because the blue component signals to the plant that it is out in the open, that is it's not in the shade of a plant canopy, and this keeps the internodes short, which is important for cannabis growers, but not for vegetable growers. Almost all growlights are sold to provide for the indoor cannabis grower, and that's why the emphasis on 6500K. Cheers.
Paul Mozarowski.


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RE: newbie confused on T5 specs

To fire Chlorophyll A and Chlorophyll B you need red light and blue light. It takes all the colors of the spectrum to make photosynthesis and fire the light harvesting complexes in the thylakoid membranes in the leaf. This is called "photobiology". Evolution says what plants need, not Man! We didn't reinvent photosynthesis with your half baked fluorescents which don't replicate Sunlight or behave like Sunlight behaves.

FL weren't meant to grow plants at all, and they're just warehouse lights you brought into your growrooms. Status quo growing makes you think that what you have is acceptable. People used to think cassettes and LP's made the best sound too, until CD's came along. It's perceptions of good. Everything grew with the full spectrum, high intensity, high frequency, plasma made Sun. Cannabis has nothing to do with anything. All living things on Earth evolved with the Sun. Go read up on your photobiology.


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RE: newbie confused on T5 specs

flouros arnt crap at all, ive been growing 3 watermelon plants per 4ft 2 bulb fixture and i got 6 watermelon, and 6 cucumbers, but i guess its because flouros couldnt be anymore perfect for low growing plants.


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Photons of any wavelength just as good, not just sun

Please check botany online before making blanket statement about chlorophyll. Plant has many other pigments that it uses to capture ALL different wavelength, so EVEN WAREHOUSE LAMPS are all excellent to grow with. Just please don't use a mercury vapor lamp, they really aren't that much good, but fluoros are excellent, HPS is excellent, MH is good, any light that delivers lots of photons is fine. Paul Mozarowski.

Here is a link that might be useful: photosynthesis quantum yield, any wavelength will grow a plant, and I am doing it currently using WAREHOUSE lamps - the plants love it, thank you very much.


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RE: newbie confused on T5 specs

You might find this reference more appropriate since it includes an actual measured action spectrum for plants (the graph is not as pretty though!). This graph is the average of 8 food crop species. I tried to find a paper including actual data which would be visible to people without a subscription but no luck so far. There have been at least half a dozen studies done on action spectra for multiple plants, and many more on single species in particular conditions.

Don't make too many extrapolations from this single graph showing green wavelengths to be more effective than blue. Other studies have been done and while the red peak is always the highest, most plants appear to show blue wavelengths slightly more effective than green, sometimes significantly more effective. Variations have also been shown for the same plant species at different times of the day or year, when grown in different conditions, and even when exposed to short-term stresses. Perhaps the most useful thing to take from this is that different light spectra may be more effective for different plants. Or my own conclusion, that within a fairly wide range, plants will use any combination of wavelengths fairly efficiently.

Algal and bacterial action curves can be radically different although they utilise more or less the same pigments as plants for photosynthesis. Some show large blue peaks, others large red peaks, others a spectrum similar to plants. Best to ignore them unless you are growing coral ;)

Here is a link that might be useful: Photosynthesis action spectrum


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