T5's come in all kinds of different outputs. A daylight bulb will be best for most plants, and will have a color temperature of 5000-6500K. CRI is usually higher in daylight bulbs, and I prefer high CRI bulbs for their more natural color.

I bought my T5's from that site last fall. Ushio is a respected brand, but I went with TCP because their 6-pack is the same price as Ushio's 4-pack. I've been running 8 of the 6500K TCP bulbs and I'm very happy with them. I was a bit worried about shipping fluorescent bulbs, but they were packaged very well.

Thanks penfold2. Any truth to their 104 lumens per watt claim? That's 11.5 more lumens than they are technically supposed to output. Was that a mistake on their part or do Ushio/TCP lamps actually emit slightly more lumens than competing brands?

Another question: If I wanted to mix it up with some red/far-red lamps, what would be the recommended Kelvin rating? I'm guessing that for full spectrum lighting, an 8 lamp unit would be comprised of mostly 6500k, but also have some number of red lamps at a given spectrum. Should the ratio of 6500k, and let's say 4100k lamps be even?

Different bulbs will have different lumen outputs, there's no standard. As for whether these bulbs have slightly higher lumen outputs than other daylight bulbs, I don't know. I don't take lumen ratings too seriously since they are rarely listed as exact readings and tend to vary between different sources.

I can't answer your question about red/far-red supplementation since I use all 6500K bulbs. I get plenty of compact growth and flowers on my plants, so I have no desire to experiment with additional red light. One thing you should realize though, is that most bulbs use a similar, if not identical, phosphor blend to achieve a full spectrum. They just vary the proportion of the phosphors to output more strongly in different areas of the spectrum, thus creating different color temperatures. So mixing 6500K and 4100K bulbs won't be much different than using all 5000K bulbs.

I don't know if that helps much, but a lot of people seem to have the mistaken idea that mixing bulbs fills in missing bands in the spectrum. As if high kelvin bulbs only produce blue light and low kelvin bulbs only produce red light.

Can you provide evidence for that opinion? I just find it hard to believe that there are many available Kelvin ratings for these lamps for no purpose. Whether fluorescent, HPS, MH, there has been significant evidence that blue light encourages chlorophyll absoroption, red light promotes photosynthesis, and far red light boosts flowering. In terms of HO fluorescents, every piece of literature I come across suggests to mix cool white and warm white for full spectrum lighting.

Perhaps there is some truth to both arguments. Perhaps an even mix doesn't really provide optimal results, but 1 warm white red spectrum in a mix of 5 cool white blue spectrum bulbs yields something better for vegetative growth while the reverse will have a better effect on the floral stage. I'm not sure, but I'm curious to see what you have to say on the topic. I am aware that some plants will flower with strictly 6500k lighting, but maybe this is not the "best" light for flowering.

@yukatan, I use half red(3000k) and half blue(6500k). I've always assumed that using both ends of the spectrum delivers a "full spectrum". I don't have any evidence to prove one way or another, but it works for me.

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Well I was trying not to suggest a "best" spectrum, because that is a huge debate that never gets definitively answered. I use 6500K bulbs because they are a good approximation of natural sunlight, and I get good results from them. If you feel that 5000K or 4100K is better for your purposes, then by all means use those bulbs.

What I was trying to say is that there is no inherent advantage in mixing bulbs. For example, there is no benefit to using urban's 6500/3000K bulb combination if you can find 5000K bulbs. The 6500/3000 combination will average out to 4750K, which is nearly identical to the 5000K bulb. If you feel there is a significant advantage to be gained by adjusting color temperature to specific values in between those offered by a single bulb type, then mix away. But since these come in packs, you might save some money by sticking with one bulb type.

Whichever bulbs you choose, I think you found a good place to buy them. I would never pay "grow bulb" prices when you can get bulbs with identical performance for a few dollars apiece.

@urban: You have a nice setup and very nice plants, but none of the plants in the picture (lettuces and basil) are meant to flower. We would have some proof if you had roses and tomatoes flowering and fruiting under those plants as opposed to the same setup with all 6500k lamps.

The sun emits a K rating closest to 6500K bulbs, yet all of these light websites preach mixing 6500k and 3000k, or a comparable bulb, for full-spectrum lighting. Wouldn't full-spectrum be exactly what the sun emits for plants? I would like to hear more of your thoughts about this.

@penfold2: First, I want to say thanks for the conversation. Your input is helpful. While I understand what you are saying, I still think that there is more to it than simply averaging out the K. Price is not a problem when mixing HO Fluorescent bulbs because 6500k and 3000k options are the same price. Now, I'm not preaching you should use a blue/red combination, but maybe all blue is better during the vegetative stage, while one red and one blue or all red is good for the flowering stage. It's just an idea. I am still learning too. I'm saying this because I have seen positive proof that red spectrum bulbs at a certain K rating and nm wavelength induce flowering. Wein's law has something to do with it, e.g. 3,000,000 / K rating = nm wavelength (3,000,000 / 4100 K = 731 nm) 731 nm is at the peak of the far-red wavelength which has shown the best flowering results for plants grown strictly with lights. Graphs actually peak at that mark via led-grow-master.com.

These are all tri-phosphor bulbs that we're looking at. Each phosphor covers a different area of the spectrum, and by combining all three you get a full spectrum bulb. If you look at the spec sheets on TCP's website you can see the spectral output for each bulb. You'll see that all of the bulbs have spikes at around 435, 540, and 610 nm. These are the same three phosphors being used in all of their bulbs. They just change the proportion to shift the color temperature one direction or the other. So by combining different bulbs, you are just averaging the phosphor ratios. If you were to find a bulb that used a very different set of phosphors, there may be some benefit to its addition, but I think most full spectrum bulbs use a similar tri-phosphor blend. GE's T5's show similar spikes.

My point was that these are all full spectrum bulbs. You don't need to combine different bulbs to achieve a full spectrum. 6500K bulbs still supply red light and 3000K bulbs still supply blue light, just different ratios. If you feel that changing the ratio at different growth stages is beneficial, then I can see why you might want a couple 3000K bulbs.

If you really want to experiment with red/far-red supplementation, you might consider a small LED light over a portion of your grow area. LEDs have very tight spectral outputs and come in a wide range of colors. You could probably find one with an output strictly in the 620-750 nm range.

My point was that these are all full spectrum bulbs.

Does this

look like this

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to you?

Full spectrum simply means they are not missing any portion of the visible spectrum. As for approximating sunlight, the 6500K bulb does a better job of that than the 3000K that you showed, which is why I use 6500K bulbs. Also, all artificial light sources are spikey by nature, especially fluorescent, so you have to accept some compromises when using them. Luckily, plants don't seem to mind too much as long as we select reasonable spectrums.

@penfold2: I still don't think it's the same. The further you move towards 6500k, red light is emitted at a lower intensity. For instance, in the charts you provided on TCP/GE, there is only one far-red peak at 6500k and five far-red peaks at 3000k. The thickness of these peaks also has a lot to do with the spectral output. At 3000k, the red band is much thicker than the same measurement at 6500k, so you're recieving significantly more red light than the vertical peak can show alone. The same is true when comparing the thinner blue band at 3000k with the thicker measurement at 6500k. Thus, it is better to mix 6500k and 3000k than to supply an even 4700k. At 4700k, the 3 main spikes will all be fairly equal in height and much thinner. You'll be receiving far less blue, red and far-red than you would if you mixed 6500k and 3000k. By using 6500k alone, you will receive far less red and far-red light than you would if you mixed it with 3000k and in addition, you also wouldn't lose any of that beneficial blue light.

The bands appear to be the same widths to me, just taller in the expected areas for each bulb. I think if you averaged the spectral distributions for the 6500K and 3000K bulbs, you'd get something that looks very similar to the 5000K distribution. I'm sure you'll get good results either way though, so buy whatever you feel is best.

BTW, I believe far-red light is considered to be in the 680-750nm range, so these bulbs seem to have only one significant far-red spike at ~710nm.

Look at the GE website. It displays a better image for comparing all K ratings on the same page.

And yes, it's true. Far red peaks at 730 nm. No matter how small the peak is at this range for all k ratings, there are clear increases in the number of peaks and width of these peaks as you lower the k rating towards 3000k. More peaks, higher peaks, and wider peaks = more of that particular spectrum in that particular bulb.

Full spectrum simply means they are not missing any portion of the visible spectrum.

1. If that is what it means, why are you even mentioning "full spectrum" in a plant growth context?

2. The triphosphor bulbs are practically missing light from 640 to 700 nm.

3. Compare with older type cool and warm white:

all artificial light sources are Spikey by nature,

No, light from incandescent bulbs is artificial and not spiky.

1. If that is what it means, why are you even mentioning "full spectrum" in a plant growth context?

Because yucatan seemed to want a full spectrum bulb with a higher percentage of red than natural sunlight.

2. The triphosphor bulbs are practically missing light from 640 to 700 nm.

That does appear to be their biggest deficiency, but they have a strong output around 610nm which, while not as efficient as the 640+ range, is still quite useful to plants.

3. Compare with older type cool and warm white:

You've spurred me to read up on phosphors. It's my understanding that the older halophosphate bulbs are being phased out in favor of more efficient and longer lasting tri-phosphor bulbs. I have not been able to find an HO T5 with a spectral distribution like you showed above. The only "cool white" HO T5 I found (Philips F54T5/841/HO/ALTO) is a tri-phosphor bulb with a corresponding spectral distribution. What T5 bulbs would you suggest using?

No, light from incandescent bulbs is artificial and not spiky.

I generally ignore incandescent light because it's too inefficient to be used for horticulture.

Because yucatan seemed to want a full spectrum bulb with a higher percentage of red than natural sunlight.

If someone says "hot dog" at a vet's office, they have every right to mean a canine with a fever. Thusly, yucatan could have meant a spectrum that is full for better plant growth.

That does appear to be their biggest deficiency, but they have a strong output around 610nm which, while not as efficient as the 640+ range, is still quite useful to plants

No, it doesn't have enough far red. That spike at 710 isn't enough. I would like to show you the spectral density chart for Sylvania Gro-Lux Wide Spectrum, but I am having trouble locating it. Until I find it, you can take my word for it that it has much more far red than those triphosphors.

What T5 bulbs would you suggest using?

I'm not. I am suggesting that anyone with those phosphors test the addition of 34% of the fluorescent wattage (or 25% of the total wattage) as incandescent. Just as test, and, if it doesn't improve growth or makes the plants too spindly, tell everyone.

I generally ignore incandescent light because it's too inefficient to be used for horticulture.

If you never tried it, then that is what is called "Begging the Question".

I never wanted a full spectrum bulb with a higher percentage of red than natural sunlight. I wanted the optimal mix of red and blue for full spectrum growth and to understand why mixing is better than using only blue. It seems that with some research, I have answered my own question.

penfold, the chart shown above illustrates the spectrum of 40 watt Standard T12's, not 54 watt HO T5's.

struw, this is the second time you have hijacked my thread in an attempt to insult someone. please stop or i will contact the moderators for the second time.

Struw,

For my purposes anyway, it seems I have sufficient red/far-red light to allow healthy growth habits in my plants. But I can see how some far-red supplementation may be beneficial as long as the red:far-red ratio doesn't drop to the point of causing undesirable growth habits like etiolation. I wouldn't use incandescents for anything more than testing purposes, though. They are proven to be one of the least efficient forms of artificial light.

yucatan,

I know the charts above were for T12's. I was just wondering if they were applicable to HO T5's since that is what we're talking about. It seems tri-phosphors and expensive grow bulbs are the only options I see. As for spectrum, I do think the 6500K's are the closest approximation of sunlight, but I wish you luck even if we don't agree on that.

struw, this is the second time you have hijacked my thread in an attempt to insult someone. please stop or i will contact the moderators for the second time.

I suspect that you have mistaken constructive criticism for an attempt to insult. Whom have I attempted to insult? Did I succeed? The moderators will require that information from you before they can take action. But, thank you so much for confessing that you like to jump on flimsy opportunities to complain to the moderators.

I wouldn't use incandescents for anything more than testing purposes, though.

Have you tested incandescents and, if not, will you?

BTW, did I insult you?

I couldn't find the spectral density chart for Sylvania Gro-Lux Wide Spectrum, but, here is a similar lamp made by General-Electric:

As I recall, the only outstanding difference was in the blue region (Gro-Lux WS had more blue). As you can see, these had a substantial amount of far red. The Gro-Lux WS were good lamps when new, but deteriorated rapidly with age.

Have you tested incandescents and, if not, will you?

I have not tested incandescents, but I may try it for the next month or so before my plants go outside. I was referring to their low lumens/watt rating before. I see from looking at the spectrum now that they are very high in red light and beyond, but LEDs might make a better long term source if you could find them in the proper spectrum.

BTW, did I insult you?

I can see where some may find you a bit brash at times, but I took no insult. I have pretty thick skin.

I couldn't find the spectral density chart for Sylvania Gro-Lux Wide Spectrum, but, here is a similar lamp made by General-Electric:

That looks nice in the upper region, but needs quite a bit more blue I think. I grow specimen plants, not crop plants, so compact growth is very important to me. Also, these are all very old T12's. I haven't been able to find those old halophophors in newer technologies like T5's. I also wonder about the phosphor lifespan. Replacing bulbs every growing season would be wasteful and potentially expensive if it were necessary.

I grow specimen plants, not crop plants, so compact growth is very important to me.

The internode distance of potted ornamental plants can be controlled with a soil drench of a solution of the plant growth regulators, Arest, Bonzi or Sumagic. If you shop, you can get them cheaper.

@yucatan, here's some relleno peppers grown under that light, at the same time.

My thoughts on the light spectrum are simply this, I think by splitting the two ends of the spectrum with different bulbs, you are giving the plants more to work with in color. I know that's not "scientific evidence", but I know plants and they respond well to it.

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I used to use a combination of 6500K and 3000K bulbs but have switched them all to GE sunstick 5000K bulbs and I'm satisfied with the outcome. Of course I have also overdriven the bulbs by about 60% by using dual T12 bulb fixtures and using 4 bulb T8 Ballasts. My plants look better than they did last year.

Do you think they look better because you changed bulbs or because you added 60% more light. I think it's time for an experiment :~)

With all conditions the same, put me down in the mixed spectrum club. I think that harnessing the extremes by combining red and blue bulbs gives more coverage than the relatively weak middle of the spectrum, which is closer to yellow light.

GE sunstick

That probably should be "GE Sunshine" or "Sylvania Sunstick."

Incidentally, it is much more difficult to find power spectral density charts for fluorescent bulbs than it was 30 years ago. Now, light bulb manufactures seem to want to keep consumers in the dark. (pun intended) It must have something to do with the new morality.

Good point yucatan!

This is off topic but what the heck, it is a garden forum. Check out this pic of my garage grow room, 2,016 watts and 218,400 lumens! It's like a giant tanning booth :~)

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@urban: 1, 400-watt Metal Halide Lamp yields 50,000 lumens. This ouput is equivalent to 10, 4-ft. High Output T5 lamps. So you have approximately 44, 4-ft. High Output T5 lamps in that room? Don't get me wrong, I'm envious, but I would never pay for that many lamps out of my own pocket. If I was growing on that scale, I'd have 2 HPS, 2 MH and 2 fluorescent's for seedlings.

An interesting find related to our discussion here:

"A key part of our research involved the determination of which light frequencies or wavelengths would produce superior plant growth results."

http://www.patentstorm.us/patents/6921182/description.html

Since LED's represent a relatively narrow band of light, as opposed to HID's or Fluoro's, the researcher's used these lights for accuracy purposes. Prior research that they found gave a broad suggested range within bands 620-680, or 700-760 nm (red) and 400-500 nm (blue).
After a year and a half of research, they settled on three more specific light wavelengths that produced the best plant growth results.

"660 nanometers (nm) is the wavelength that drives the engine of the photosynthetic process. The 680 nm wavelength is perhaps closer to the peak absorption wavelength of one of the two chlorophylls found in higher plants. However, at 680 nm you miss completely the absorption curve of the second chlorophyll, and furthermore the output curve of a 680 nm LED has a fair amount of light output above 700 nm, which is known to cause unwanted morphological changes to plants. LEDs of 680 nm output are also rare in the marketplace, making them relatively expensive. Our choice of a 660 nm first wavelength component is a compromise wavelength commonly used in plant growing research, which supplies energy to both types of chlorophyll without emitting enough light above 700 nm to adversely affect plant growth.

The 620 nm LEDs used in the aforesaid Ignatius et al. patents, are meant to provide the light energy for photosynthesis, but a look at the absorption spectrum for the two chlorophylls shows that this wavelength falls almost entirely outside the absorption curve for chlorophyll.

Our research showed better results using LEDs of 660 nm and 612 nm rather than the wavelengths of 620 nm and 680 nm. Beneficially, LEDs of 660 nm are also readily available in the market, and are very inexpensive.

Our second 612 nm wavelength component was selected not to promote photosynthesis, but to match one of the peaks of the carotenoids. As noted in "Influence of UV-B irradiation on the carotenoid content of Vitis vinifera tissues," C. C. Steel and M. Keller (http://bst.portlandpress.com/bst/028/0883/bst028883.htm), "carotenoid synthesis . . . is dependent upon the wavelength of visible light, and is diminished under yellow and red filters."

By providing the orange 612 nm light, we not only promote creation of carotenoids, which are required for plant health, but also add a little to photosynthesis, since the carotenoids pass their absorbed energy to chlorophyll. Carotenoids are required for plant health due to their ability to absorb destructive free radicals, both from solar damage and from chlorophyll production, whose precursors will damage plant tissue in the absence of the carotenoids. During research we found that, beneficially, test plants turned a deeper green, i.e. produced more chlorophyll, with the addition of our 612 nm light component. This ability to increase a plant's chlorophyll content with this specific light wavelength is an important aspect of our invention.

Blue light of about 465 nm, this wavelength being non-critical, is strongly absorbed by most of the plant pigments, but is preferably included as the third component in our lamp to support proper photomorphogenesis, or plant development. Any LED near this wavelength will work as well, but the 470 nm LEDs are commonly available and less expensive than many other blue LEDs.

Regarding the proper proportion for each wavelength, it is known, from independent laboratory research, that a blue/red proportion of 6-8% blue to red is optimal. In sunlight the blue/red light proportion is about 30%, but this is not required by plants. More than 8% blue light provides no additional benefit, but adds to the cost of the device since blue LEDs are among the most expensive to manufacture. In our device we include about 8% blue light, which is near optimal for plant development while offering the greatest cost savings. Our research showed that best results were obtained when the output of the 612 nm orange LEDs in our device was added to the output of the 660 nm red LEDs when calculating our most desired blue/red proportion."

"Do you think they look better because you changed bulbs or because you added 60% more light"

I think it's from 60% more light. The plants are a little more compact.

" That probably should be "GE Sunshine" or "Sylvania Sunstick.""

My mistake, they are Sylvania Sunstick.

What sellers on eBay and such usually call "red" and "blue" are just normal lamps (3000k/6500k) .. certainly NOT "red" / "blue"

Sorry for the rant here, but:
3000k is just normal "warm white"
6500k is just normal "daylight"
you can also get T5's in any of the other "normal colors" like 4100k or 5000k. (I've even seen gro-lux-ish colored, and ofcourse various aquarium lamps)

And yes you can get true "Red" and "Blue" T5's .. For 4' HO T5 those would be:
F54T5/RED (looks more pink when lit unlike "red" T12 lamps which truly light red...but are quite dim)
F54T5/BLUE
Don't know how It'd turn out, but I could probably attempt to upload a pic of them.

You guys should really be throwing in some "blue" lighting for that lettuce if you want it to have actual flavor and color. Not just yellow and white light. Yuck!

Hi,
I know this thread is pretty old and might be non responsive now, but if any one of you is still available, I want some help regarding choosing the ideal grow light for growing iceberg lettuce through hydroponics indoors. It would be great if you could suggest me the light to be bought.

Thanks

My experience with Strip Lighting is that T12 are older but very cheap lights to use for a Planted Tank. They have cool white at 4100k-5000-6500k with High Lumens.

I also tried buying 2 T8 bulbs & what I found out is when I use one 35 watt T8 at 3500-4100k my plants start pearling letting off a lot of bubbles, oxygen released.

If I simply add two T8 bulbs with 5000 or 6500k my plants to grow but don't seem to ever pearl. BUT when I've added One T8 4100k with one T8 5000k I've got plants that pearl letting bubbles out all day long.

My guess is that the 3500-4100k bulbs are putting out more Red/Orange wave length that Plants love but might not look great for viewing.

So best thing to do is buy a strip light that has 4 bulbs in one unit or buy 2 dual strip lights so you can have:

4 Bulb Strip Lighting for great plant growth
1st bulb at 5000-6500k a clear white for better viewing that has high lumens.
2nd bulb at 3500-4100k cool white for plant growth ( that has more red waves)
3rd bulb (buy a Philips 4ft T8 32 watt Plant & Aquatic Linear Fluorescent Bulb)
4th bulb actinic blue light for great plant growth.

Most of these bulbs are cheaper ranging from $6.00-20.00 per bulb.
Actual strip light housing can be bought for $9.99 & up

Same thing goes for T5 HO bulbs-
They have color ranges from 3500,4100,5000,6500,7000,10,000 etc.