Hi John! The best deal I was able to find was at goodmart.com about 5 months ago. However, there is a minimum order of 12 tubes @ $82.80 plus $5 shipping - so I don't know if this will help you. All of the Internet sites carrying this lamp had a minimum number of lamps to order. (I also had the same dilema with local Home Depots no longer supplying Osram Sylvania). I got much better results by mixing the Gro Lux Aq with GE Chroma 75 (1:1).

John_Z.

Jon K,

Apparently Aubuchon likes to sell Sylvania Gro-Lux bulbs in lots of 6. They might be available in a local Aubuchon Hardware.

MM

MM, thank you for sharing this site; I know several people that don't want to buy in the quantity of lamps I need during the cool months.

I mentioned using the Sylvania GRO LUX with GE Chroma 75, but didn't say why. Over the past 5 months I noticed much better foliage and flower development on numerous species using this combination. (I'd never make the mistake of using "WS" again with the Sylvania tube as I did years ago). It's important to experiment and observe. This cool white and warm white jargon that many use on this forum overlooks the absorption spectra that plant pigments require vs. what the lamps actually emit. Short term results are not the same with growing under lights for 6 - 8 months or more.

Happy growing!

Thanks for the sources, John Z and Maine Man. Goodmart.com seems to have the best price on the gro-lux tubes, even when you factor in shipping, so I'll probably order from them the next time I need them, although there are Aubuchons within driving distance of my house, so I can use them in a pinch.

That being said, I have another question if you'll indulge me. I hope I'm not taking advantage of your expertise ;)

Hmm, how to make a long story short? ;)

Okay, so I have a light stand which I use to grow African Violets and foliage plants. Each fixture holds 4 tubes.

For a while now, I've been using 2 Colortone 50's, 1 "daylight," and 1 gro-lux standard in each fixture (don't ask me how I arrived at that combination). I'm fairly satisfied with the color rendition, but less than satisfied with the growth.

I've been thinking about buying Agrosuns and using 3 of those along with 1 gro-lux in each fixture -- I use 1 gro-lux mainly because I like the way it deepens the colors of the African Violet flowers just a little -- BUT the cheapest I can find them for is $14.99, not including shipping, and you have to buy six of them. That's a little much for my budget. The color temperature is 5850K and the CRI is 93.

Now, yesterday I came across a web site, fullspectrumsolutions.com , which makes a brand of full-spectrum fluorescent tubes called Paralite. Under the Paralite brand is a bulb called the "Spectra 5900." It has a color temperature of 5900K (very close to the Agrosun, only a 50 degree difference) and a CRI of 93 (same as the Agrosun). It also has a whopping 2500 lumens per bulb, which is good for me because I can keep the lights further away from my African Violets, which keeps them cooler, AND the cost is only $6.75 per bulb when you purchase 6.

My question is: Would the Spectra 5900 be similar in light quality to the Agrosun because the color temperature and the CRI's are so close to each other? I don't know if you can make that assumption or not.

John Z, I know you suggested using 2 GE Chroma 75's and 2 gro-lux standards, but at 1900 (I think) lumens for the Chroma 75's and 1200 lumens for the gro-lux, I don't think that would provide me with the intensity of light I like to have so that I can keep the lights a good distance away from my African violets, both to keep them cooler and to make them more visible (If they're up too close to the lights, the hood of the fixtures obstructs your view of the flowers).

Thanks for any input you can give me, if you have the time.

- Jon K

Jon, don't get too hung up on the lumens. Lumens are for humans, not for plants. Green light scores more lumens than the same amount of red or blue light. Lamps with lots of far red and blue light are great for plants but look terrible to out eyes, score low lumens even though they are putting out just as much light as other lamps, and can have a terrible CRI.

High-CRI bulbs may or may not be better for your plants. Some high-CRI bulbs just produce a big spread of green light but nothing extra at the red end, which means no extra benefit for the plants. Some high-CRI bulbs extend the red end of the spectrum, which means benefit for the plants. A rule of thumb is that high CRI and high lumens means they just boosted the green and the bulb is probably no better than a mix of cool whites and warm whites.

I can find no reliable documentation of the actual spectral output for the paralites. Their own documentation looks very dodgy to me. The one spectral curve I found that might be realistic showed a typical triphosphor cutoff at 520nm and a boosted yellow/green portion of the spectrum. Based on what I've seen I don't think this lamp would be any improvement over your existing setup.

Hi guys, I just picked up a couple of grow-lux/AQ tubes (wide spectrum) at Benny's in Seekonk (or maybe Attleboro) I'm not sure if you have a Benny's near you but they were 5.99$ each.

Hi Jon! You mentioned being fairly satisfied with the CRI of your present tubes, but less than satisfied with the growth of your plants. Of course, we need to consider all the cultural and environmental factors to determine what the problem is(fertilization, potting media pH, etc.) not just the lamps.

Brace yourself for some technical terms, but understanding them will make all the difference in choosing lamps. I was confused at first years ago, so don't feel alone if it happens.

There are 3 considerations in choosing lamps for plants, vs. lighting for the human eye: PAR, PPFD, and the duration of both. Let me explain. PAR (photosynthetically active radiation) are the violet, blue, and red wavelengths needed by the "higher" plants that most of us grow. These wavelengths appear dim our eyes even at high wattage or lumens, so "bright" lamps are an eye thing irrelevant to plants. The amount of the colours/wavelengths ROYGBIV in a lamps is revealed by its "spectral power distribution" graph (SPD). The company who makes the lamps will often fax the SPD graph to you if you cannot find it on the Internet. I've got piles of them. By keying in on your browser, "spectral power distribution of sylvania fluorescent lamps" you can see examples of what I'm talking about.

Then I compare these lamp graphs to the "absorption spectra" of plant pigments, namely chlorophyll a, chlorophyll b, and the carotenoids - particularly beta-carotene. Plant pigments will either reflect off the wavelengths that your lamps provide or will absorb them for photosynthesis. They reflect off most of the green, yellow-green, yellow, and yellow-orange wavelengths that just so happen to appear as bright to human eyes. Absorption spectra graphs reveal that violet, blue, and red (PAR) are what are needed for photosynthesis, and CRI of lamps don't indicate what colour wavelengths are in a specific tube. "Cool white" and "warm whiate" terminology is equally useless! Light intensity in watts or lumens do not refer to how much PAR is available to a plant, and is also irrelevant to how much PPFD (explained next) exists.

The measurement of how many usable photosynthetic wavelengths actually reaching the leaves (its density) is called PPFD, or photosynthetic photon flux density. This is about usable photons. And if the PPFD is not enough in your lamps when the PAR is relatively good, many plants can make up their need for a daily amount of carbohydrate production just by settin the light timer to remain on another 2-3 hours.

This can be a lot to digest, so I'm going to stop here. Again, feel free to let me know what you can't grasp.

Respectfully, John_Z.

Just one correction: PAR is defined as the radiation within the 400nm-700nm range. It is not just the violet, blue, and red wavelength, nor is it weighted in any other way to the wavelength pf the light. PAR considers green to be equal to red or blue. PAR itself cannot be measured since it is just a descriptive term. PPFD is the measured unit of PAR, usually in micro-moles per second per square metre.

To be a little more precise, PPFD is actually the photon count between 400nm and 700nm per unit area in a given time. Occasionally a range of 300nm-700nm or 400nm-800nm is used for particular experiments. It is interesting to note that one photon of blue light contains nearly twice as much energy as one photon of red light.

So PAR and PPFD are only a rough approximation to the light that plants actually need, but it is a better measure than lumens, which are weighted towards light for humans, not for plants. Unfortunately, PAR and PPFD numbers are not available for most fluorescent lamps, not even for many metal halide or HPS lamps. Many technical aquarium and plant growing sites do have PPFD or PAR numbers.

Shrubs, you are correct that the 400-700 nm range is defined as PAR. I know that. But Jon is growing Saintpaulia, not cyanobacteria which absorb better in the mid region of the spectra using bacteriochlorophylls a through e. I didn't want to add too much at first by throwing in the micro-moles per second per square metre. LOL.

Sure John, but it matters because PAR doesn't measure the light that is important to plants. A single-wavelength green LED produces as much PAR light as a blue or red LED, but you wouldn't want to use it as a plant light. PAR is a poor measure of how good a lamp is for plants. The only reason that we use it at all is that it is better than lumens, which would tell you that the green LED is actually better than the red or blue one :)

To take things even more at a tangent, PAR will sometimes look bad for a light that is actually good for plants. A fluorescent phosphor that produces a good light peak at 650nm usually produces a good chunk of light beyond 700nm which is considered "dead light" by PAR, whereas a phosphor that produces no light beyond 700nm looks good on PAR but does not produce much useful light at 650nm. The same is true at the blue end where the 400nm PAR limit is barely beyond the 410nm-420nm light that you want for plants.

One last thing, if you look at PAR numbers for different fluorescents, they are all the same! Seriously, the amount of light, counting all wavelengths equally, is pretty close to the same for all the fluorescent lights where I can find the data. Since I realised this, I don't really care to look for PAR data any more. I look for a spectral graph, or try to estimate one from the temp and CRI numbers, and a guess of the phosphor.

OK. I guess I shouldn't keep this one to myself, but if you go here, you can see what phosphors Philips uses for each color temp and CRI type, including their CLF's.

Once you get to this page you can choose from several types of fluorescent lamps, and then download the phosphor data sheet, with graph, for each major color band.

The URL is long, so you might have trouble getting all of it in the address bar. These are really nice looking PDF files.

http://www.lighting.philips.com/gl_en/global_sites/lighting/phosphors/applications/lighting/assortment.php?main=global&parent=3706&id=gl_en_phosphors&lang=en

Zink

Here is a link that might be useful: Philips Phosphor Data Sheets for Fluorescents

Zink, thank you for sharing that site. I'll get to back to it shortly, although I kept getting "page not available" when trying to click onto the phosphor specifics.

Shrubs_ bulbs, I admit being confused about statements in your posting on 2-25. For example, you said that, "PAR doesn't measure the light that is important for plants". I'm aware that PAR includes the visible range of 400-700 nm by commonly used definition, and it is measurable in terms of PPFD. We must consider that photosynthetically available and usable radiation from any light source is also plant-specific because of varying plant pigments in autotropic life forms from different Kingdoms and Families. No doubt, the efficiency of photosynthesis is not constant for all wavelengths as implied by the definition of PAR. As I said, in context to what Jon's interests are - we are talking about the Saintpaulia genus, not algae, cyanobacteria, or some creature from the Black Lagoon. LOL. True, the importance of PPFD is not to be underestimated. PAR, PPFD, and the duration of both, as I said earlier, are 3 considerations. I just didn't get to the PPFD part yet with Jon.

As for the "PAR numbers" for different lamps being all the same, I honestly don't know what you mean by that. I compare the SPD of lamps to the absorption spectra of higher plant pigments, and suggest to others that they do the same. Why? You get significantly different results in terms of plant appearance, health, and longevity when you get to the specifics of the CRI, "cool white", and "warm white" jargon. Lamp CRI to me only suggests that I consider examining the lamp's SPD graph to see if there is sufficient irradiation from the violet, blue, and red spectrum to match a plant's absorption spectrum.

CRI ratings in themselves can be enormously deceptive if you want to consider usable PAR emissions from lamps. At the same time, I don't underestimate CRI needs for those concerned about plant display and visual appearance.

I apologize for throwing that website information right into the middle of your discussion. It was late, my mind was starting to skip dimensions, Hagbard Celine was starting to infiltrate Skylark DuQuesne, a solid dreamscape was forming - you get the idea... or maybe not.

I just thought it would be a good discussion diverter. Actually, there were a few peculiarities on that site I hadn't mentioned.

For instance, first my browser comes up with a message:
This content is only available in an alternative language.
Please confirm that you agree to switch this alternative language

Just click on Agree, and nothing unusual happens  it keeps on giving you English.

John ZÂ When you click on the phosphor TYPE, you end up with a PAGE NOT FOUND error. The key is to click on the phosphor CODENUMBER, instead. Then you get end up with a beautiful PDF.

Try it again.

Zink

Here is a link that might be useful: Philips Phosphor Data Sheets for Fluorescents

Hey Zink! Clicking the code numbers worked! I really appreciated seeing the emission spectra of the phosphors on a graph too. The phosphors are one aspect of growing under lights I hadn't looked into until now. Fascinating. And by the way, no need to apologise for interjecting something relevant to tubes.

I'm trying to gather more info on ideal PPFD ranges for specific species under light. (There is a conversion factor from foot-candles to micromoles/sq.meter/sec. using natural light, but I cannot find any reliable info for artificial light except for aquatic plants (which I don't use in my aquarium). So far there is little data available, and it is very inconsistent and contradictory. But I consider the source: it's coming from commercial sources. Also, perhaps there has not been comprehensive studies done - I don't know. Does anyone?

There is no conversion from foot-candles to PPFD without knowing a full spectral distribution. They are really two different things.

PPFD is the number of photons with wavelengths between 400nm and 700nm hitting each square metre each second.

Foot-candles are lumens/square-foot. Lumens are calculated as a weighted sum of the luminous flux at all wavelengths. I have linked to a table that shows the weighting at each wavelength. Note that luminous efficacy in the table is calculated from the flux in watts, not from the number of photons in micromoles. The flux per photon is equal to Planks constant divided by the wavelength of the photon.

If you knew the full spectral distribution of a light source you could calculate from one unit to the other. There is no general conversion for artificial light since it depends completelely on the spectral distribution. Any conversion that you saw for natural light would be for a specific natural light condition such as direct tropical sunlight at noon, or more likely for a black body at a particular temperature.

Here is a link that might be useful: Luminous efficacy table

Shrubs_n_ bulbs, you last paragraph particularly confirmed my suspicions all along, considering that the spectral distribution of lamps is so diverse. I think it requires a spectroradiameter to know the PPFD is for artificial light, and of course you could see how PPFD diminishes over time under fluorescent tubes.

Perhaps a new thread would be appropriate, but I'll share this anyway here. It has been a matter of experiment and observation (without a spectroradiameter) to see which species acclimate and perform well, and which simply do not over a 6-7 month period. I have Pentas lanceolata potted-up from my garden for the 4th year now, and the spectral combination I'm using now promoted excellent blooming througout the winter. It was only "okay" using Chroma 50 & Gro lux last year, the Chroma 75 along with being new tubes made a hugh difference. Adenium obesium, normally requiring full sun, is full of new foliage and flowers too, yet they are on the same growing shelves as partial sun and shade lovers - all doing equally well. My desert cacti, however, are in a south-facing window as I'm afraid to chance their decline. Many of them are the "hairy" types like Cephalocereus, Espostoa, etc. and they really require full sun to keep their spines full.

That was a great site you linked, and thank you for sharing it.

Shrubs'n Bulbs,

Wow! I haven't been to the HyperPhysics site for a long time. They have added a lot of new info. I had never seen the ones you posted.

I discovered the HyperPhysics site before I ever started playing around with overdriving e-ballasts. I had printed 2 copies of every page they had on optics, one for home, and the other to keep at work.

I didn't bother to go back to the site until your last post here. That is one great collection of interlinked physics data! I really appreciated their explanation of multiple rainbows. I once followed a huge summer storm from Denver to Kansas City which produced a spectacular set of 4 rainbows at once. I used up the rest of my vacation film on that beauty.

That is one site everyone ought to bookmark!

Zink

John, back to your original question. There are many published studies on the responses of different plant species to light intensity. A quick scan showed ranges of about 1-50 for the compensation points and 100-1,000 for the saturation points. I'm sure there are some plants a little outside these ranges, some trees for example have saturations points beyond 10,000 foot-candles of sunlight. Most experiments are performed on small plants or individual leaves and so ignore self-shading.

I did some calculations for the conversion factor from PAR to foot-candles for different light sources. It seems like you can use five times PAR to get foot-candles, give or take a factor of two. I also calculated some extreme values for monochromatic light: 12.2 at 560nm (largest conversion factor); 9.8 at 590nm (for LPS light); 2.4 at 640nm and 0.04 at 420nm (for phoyosynthesis peaks). I'll let you ponder the effects of PAR measuring fewer blue photons for the same flux in watts.

I'll leave you with one last tidbit, some photosynthesis action spectra for different plants. I don't have access to the original paper, so unfortunately there are no species labels.

Here is a link that might be useful: Photosyntheis action spectra

I just started growing african violets with fluorescent
light tubes and the ones that came with my stand are 20 watt wide spectrum Sylvania Gro-Lux tubes. There are two on each 2 foot shelf. I was wondering if this will work.

How far away should I put the standard size african violets.

Thanks!

Zuzu, I found that the different cultivated varieties of all Saintpaulia species have different requirements for "intensities" of light, although the more correct term would be PPFD. It will be a matter of experiment. When I moved some varieties closer to the tubes gradually to acclimate them, some finally went into bloom and other began to show signs of too much light (reddening of the leaves).

There was a Web site that I can no longer find that stated the same thing - that Saintpaulias do not all respond to the same PPFD (light intensity that reaches the foliage). Given what you have stated, I would probably put them about 4 inches from the tubes, but keep an eye on them.

Also, one professional stated that the darker green varieties do better with more light than do paler green varieties. He was talking about Saintpaulia ionantha, the most commonly available ones.

If you guys are done compariing electrical engineering, I just wanted to know if the sylvania gro-lux bulbs that I got are good for my starting red bell pepper plants... or did I waste my money? it's cloudy here many days and can I supplement mother nature and use direct sunlight when possible if I keep the plants in pots?