The Octron Eco bulbs sound the best. Get one in daylight(I'd get two), and one in cool white if you're wanting to mix.

Otherwise, go to a hardware store, and buy something close to it there. I think Philips is the most widely sold line of bulbs out there. I used to use Daylight Deluxe and Cool white in a mix.

Good luck!

D.

vero,

The CRI of a lamp is indicates how well the human eye will see the colors as compared to natural light(sunlight). The better the CRI, the truer you will see colors. Plants could care less about what you see. What is important to a plant is the absorption spectrum of the chlorophyll and a few other pigments. The colors that the human eye is most sensitive to, which are centered around the green part of the spectrum, are of little use to plants.

Also, the CRI really has no direct relationship to high lumens. In fact, for most of the history of fluorescents, in order to improve the CRI (for humans, remember) the lamps required the addition of more phophors, usually more expensive, which also tended to LOWER the lumen output, while increasing CRI. There are high lumen, high CRI lamps available. It's just that there is no direct relationship between the two.

The low-lumen GRO-LUX lamps are designed to not waste energy in the GREEN area, but to output mainly in the BLUE and RED areas, where lumens have less value, but exactly where the chlorophyll absorbption range is.

To make things a little more confusing, the DELUXE versions, (DaylightDELUXE, CoolWhiteDELUXE, WarmWhiteDELUXE), all put out less lumens, but have an additional RED phosphor which is better for plants.

Actually, since most fluorescent lamps are good for plants, (some being only slightly better, or worse), and since CRI is not a consideration, the best this to do is this:
Buy the cheapest, high lumen bulb you can buy, as long as it isn't WarmWhite. The WW bulb has the least useable light of all (shrubs recently reminded me of that). The DELUXE version of WarmWhite (WWX), does have good red content, and is OK.

The exceptions to the above rule are the GRO-LUX lamps. The seemingly really dim GRO-LUX Standard has low lumens, but high plant value, as it's output is exactly in the chlorophyll absorpion ranges, not your eye's most sensitive colors.

By the way, except for infinitesimally small differences, all the major bulb manufacturers produce the exact same variety of lamps. You are really worrying more than you need to. I have used a LARGE variety of lamps, and they all seem to do well. Another Rule: The more lamps - the better.

Zink

Hi,

Thanks for your answers. Yes, I'm probably making too much fuss about which bulb to chose!

I only came to the conclusion of high CRI=high lumen because on the sylvania page I could compare 3 bulbs for which only the CRI and lumen changed (same watt, K, family (the octron eco)).

I think what I was trying to do is find a way to guess the lumen output of a bulb, as this info is usually not written on the bulb itself (you only get the wattage, and if you are lucky the CRI and K are there).

I thought the goal was to get the highest lumen and then to think about the spectrum... Now I understand that spectrum is quite important. Also, I saw that grolux comes in two variety: gro-lux and gro-lux wide spectrum. The difference is the first has peaks (around 4200 and 6500K) whereas the second has a smoother spectrum. I think the grolux (non wide spectrum) is better, am I right?

Are the deluxe versions compact fluorescent?

Thanks
Vero

Vero,

Are you asking if the compact fluorescents (the spiral type) are all "deluxe" phosphors. If so, the answer is no. Quite the opposite. I would guess that 99% of the CF's on the market are now the new, better CRI tri-phosphor bulbs.

The first compact fluorescents that manufacturers tried to sell as replacements for the incandescent lamp had such an ugly color that, in order to sell them at all, they HAD to start using the better quality (high CRI) phosphors. This wasn't too expensive to do for the manufacturers, because the overall inside surface of the small bulbs is low, compared to the common straight fluorescents, requiring less phosphor.

The GRO-LUX Standard is the dim bulb, with a smooth, 2-peak spectrum, with peaks at about 450nm and 658nm(nanometers). The GRO-LUX Wide Spectrum is brighter, and has a different spectrum containing several spikes. It appears to use a BLUE phosphor, peaking at 450nm (the BLUE phosphor used in tri-phosphor lamps) and a RED phosphor, peaking at 628nm (the same RED phosphor used in the aforementioned Deluxe lamps).

You used the figures 4200 and 6500K. The "K" value represents the "whiteness tint" of a lamp. Low K bulbs, such as the regular incandescent (2700K), are reddish-white. High K bulbs, such as a Daylight fluorescent (6500K) are blueish-white. A halogen lamp, for comparison, is about 3200K, bluer than incandescent.

The "K" value does NOT represent a specific color, only the overtone, or average color content, of the "whiteness". It is easy for two lamps which put out a completely different set of colors (meaning they put out different peaks in their spectrum), and still be the same Color Temperature, or"K". A Cool White fluorescent and a standard Metal Halide are both 4200K, but they have VERY different spectrums.

You should look up the term "metamer". Colors that appear the same, but are actually composed of different colors are METAMERS of one another. For instance, BROWN can be composed of RED+GREEN or BLUE+ORANGE or YELLOW+PURPLE. Lamps hich have the same Color Temperature, or "K", can look exactly the same, yet be composed of completely different wavelengths of light.

Zink

Hi zink,

I couldn't find a long, tubular fluorescent called Deluxe on the sylvania web site, so I thought that when you mentionned deluxe you were talking about CFLs.

Sorry I mixed the K and nm.. I should know this. But I didn't know that there was no relation between nm and K (isn't there a link? I remember from physics something like wavelenght proportional to * T^4). So why would a manufacturer make two fluorescent bulbs with the same K but different spectrum and no way for the buyer to know this (aside from calling the company to get the official spectrum output)? Or maybe it turns out that all fluorescent use the same blend of blue and red phospor (so that all fluorescent have the same spectrum peaks) but in different amounts (to get different K)? I think I'm starting to get this... if what I think is true, then there is really no better, no worse fluorescent (exactly what you mentionned in your first reply!).

I'm sorry I ask so many questions... sometimes I just need to know "why". Also glad to have learned a new word!

Thjanks again
Vero

Vero,

The link between K and nm is for blackbody radiation. This is the distribution of light given off by a warm or hot object, and the peak wavelength in nm is exactly related to the temperature in K. Fluorescents give off a different distribution of wavelengths but it is averaged out and then labelled with the temperature of the most similar blackbody radiation.

Manufacturers make bulbs with different spectrums to look better (or cheaper but not so good) for humans. All fluorescents are not made with the same exact same red and blue phosphors, but the vast majority of compact fluorescents are made with the exact same three red, green, and blue phosphors, and are called triphosphor lamps. The proportions are varied to produce a more reddish or more bluish light.

Straight fluorescent tubes are more easily available with different phosphors. The oldest design called halophosphors do not produce a very nice light for humans, it distorts colours (low CRI around 50), doesn't show reds very well, and tends to make everything look grey. A better design was produced and labelled deluxe (CRI around 80). Many straight tubes and virtually all domestic compact fluorescent now use the triphosphor phosphors (CRI 80-85). Using special (ie. expensive) blends of phosphors, fluorescents can be produced with CRI above 90 and these are used where colours must be shown accurately, for shop displays, design workshops, etc. They are also marketed for domestic use for hobbies like sewing and for use on plants. The benefits of high CRI for plants, other than making flowers look the right colour, are still debated.

The Gro-Lux fluorescent range is made with different phosphors that are better suited to plants but no so visible to humans, hence they look dim although they are producing about the same amount of light. The CRI is ridiculously low since the light looks nothing like a continuous white spectrum.

Which spectrum is best for plants? Are they all the same? There is reason to think that some wavelengths of light are better for plants than others. Plants photsynthesize best with certain wavelengths of red and blue light, although they also use other wavelengths. In addition, aspects of plant growth like height, leaf size, and flowering, are controlled by some types of blue light and particularly by the ralative levels of red and far red light. Fluorescent phosphors are mostly designed to be good for humans to see and thes happen not to be the best wavelnegths for plants. The Gro Lux designs try to produce the best wavelengths for plants. In the scheme of things, many people have tried to calculate which type of fluorescent is best for plants, with many different results. There clearly isn't a massive difference, but there does seem to be a difference.

Back to your original question about which tube to use. The Octron bulbs are clearly design for people. The Eco 32W tube is designed to produce the right amount of light for a typical domestic fluorescent application but using 32W instead of the 40W that such tubes used to use. The Supersaver Eco goes one step further and only uses 30W, but notice it produces fractionally less light and a slightly lower CRI. For plants you want maximum light so you can ignore the Supersaver Eco. The T12 produces more light because it uses more power, but you should be aware that the tubes are 50% thicker and so the light is less intense. Depending on your application, it is probably better to use the T8s, and use more of them if you need more light. You have noticed that the mean lumens is lower on the T12. Fluorescent tubes get dimmer as they get older, typically by 20% to 30% over the life of the tube. Mean lumens is the brightness you should expect at 40% of the life of the tube. The best fluorescent tubes now decrease by less than 10% over their life and you can see this with the Octron tubes. Standard practive used to be to throw out the tubes after a couple of thousand hours and replace them with a new bright tube, but this is not really necessary if you use a tube like the Octron that keeps its brightness. The Octron, btw, is a triphosphor tube. I would suggest choosing the 4100K, although you can mix and match if you like. If you want to widen your search, it is possible to find a few true 40W T8 tubes, but check that they produce around 3500 initial lumens or you might be buying an old design that just uses more electricity and doesn't produce any more light.

The Gro Lux, as I mentioned before, look dim because they are designed for plants, not people. Looking dim to people means less lumens because thats what lumens measure, but they do produce just as much light for plants. I can't tell you whether Gro Lux is definitely best. I don't use them, I get good results growing cactus and succulent seedlings under a mix of 6500K and 3000K triphosphors. Other people use Gro Lux and swear they are the greatest. Very few people grow side by side with the two types and really that is the only way to know which is best. You sound like you have an inquisitive mind, maybe you could do that and we would love to hear the results :)

vero:
I found Philips Daylight Deluxe-T8-48"-2800lumens-6500K @ Home Depot, about $3.50/bulb, even cheaper in bulk. They'll work just fine for you.