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Thread: The truth behind fluorescent light bulbs

  1. #9

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    GE's F40SP65 is by far the best cheap T-12 I have found. Forget Lumens, CRI, color temp... They don't mean squat when it comes to photosynthesis. It is all about PPFD. And GE's F40SP65 produces the most of the dozen or so bulbs I have played around with yet (about 3 times that of their plant and aquarium bulb). Incase you are wondering how I just happen to know this. Well I am graduate student studying photosynthesis, and one day I decided to bring home a quatum sensor from the lab and do a little testing. By no means a controlled study, but the F40SP65 out preformed every bulb I had. All the bulbs were the same age, or newer then the F40SP65 I was useing. Now that is model number on the bulb not the package, it can be confusing.

  2. #10

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    The aquarium tubes I bought clearly states that they are "Optimized for photosynthesis"
    (One 58 watt tube (150 cm long) costs around 20 euro.)

    Somehow I find it hard to believe that despite what the product is saying some people here claim normal lights are just as effective.
    Are you sure this isn’t your purse talking? [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile.gif[/img]
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  3. #11
    Tony Paroubek's Avatar
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    Jhupp - I beg to differ. Yes bulbs can vary considerbly, most people have only the color temperature and other published stats. It does mean something even if indirectly. Higher lumens will mean more usable light which means higher rates of photosynthesis. Color temperature indicates the color balance which will give a good basis for knowing the ratio of blue/red since most of us don't have the ability to generate spectral charts of measure PAR directly.

    The bulb your using is GE's 6500k daylight bulb. A very nice bulb indeed with excellent lumen output compared to many other 40w bulbs and shifted towards the blue so that more of the light will be usable by chlorophyll A. Especially since these bulbs are only a few bucks more than a standard cool white shoplight, they are well worth checking out.

    Tony
    Is that a Nepenthes in your pocket or you just happy to see me?

  4. #12

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    Allow me to counter. Lumens are a measure of the intesity of the bulb as precived by the human eye. It is not a measure of the amount of radiation a bulb produces. So it is quite possible to have a bulb with relativly few Lumens still generating a lot of PAR, even more so then a bulb rated with a higher Lumen output. As for color temp, this is another aesthetic measure. It is based on the temp of a theoretical balck body heated to the point where it apears the same color as the bulb. This is the reason it is given in the thermal units Kelvin. It is not a measure of the spectrum the bulb produces. As testiment to this I have the spectragraphs for a 10000 K and a 6500 K Catalina power compact in front of me, they are virtually identical. If you follow this link http://aquarium.union.rpi.edu/articles/DIY_MH.html you will find a chart listing the PPFD (PAR) for several metal hallide bulbs. You will notice vastly different PAR for bulbs of the same color temprature, indicating differences in the spectrum they produce. If the spectra were identical you would expect to see similar PAR from each bulb as spectral peaks would be in the same location and of relativly the same intensity. I say relatively, because with any value on that order of magnitude (6500, 10000,...) there is almost certainly a sizable margin of error (ie Is 6500 exaclty 6500?).

    All of the common measures that we see for bulbs (Lumens, CRI, Color Temp) are based on how we precive things illumenated by the bulb. They are not geared toward the plant hobbiest and there is really no direct correlation between them and the bulb properties we are interested in. This is an issue that confuesd me for many years. I thought, just like many hobbiest, that more Lumens meant more PAR. And while in many instances this maybe the case, it is not causal. And while I highly recomend the F40SP65, there may well be better bulbs out there. It just appears to be the best bulb that I have worked to date.

  5. #13

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    Sorry, but I drifted a little from the point of my rebutal. I can fully appreciate the fact that most people do not have the means to measure the paramters of interest to plant hobbiest (nor the funds to purchase the bulbs that are rated in this way). But my underlying point (my main point being to say I found a good bulb with valid evidence to back it up, here it is) is that we need to devorce ourselves from useing these aesthetic propeties of the bulb to infer the uesfulness of the bulb in driving photosynthesis. Simply put arguments over the best bulb based on color temp or Lumen output are without merit.

    Jay

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    Tony Paroubek's Avatar
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    While I agree to much of what you said I still maintain that they are not totally without merit despite the scales based on our perception. The kelvin scale does indicate the color of light produce by a bulb relative to sunlight. A bulb with a low rating down in the warm white area produces a large amount of red in proportion to blue. This is certainly a reasonable indicator for a standard bulb we might find on the store shelf to help compare with other commonly available bulbs. I think it's great your able to test all sorts of bulbs. Maybe you could test a whole bunch and give us some PAR values and spectral graphs so we can find the most economical bulb that will be the most benefit to our plants! But until that time all we have to go on is the other ratings from the manufacturer [img]http://www.**********.com/iB_html/non-cgi/emoticons/new/smile_h_32.gif[/img]

    How about a list of the bulbs you looked at and a PAR rating for them?? I know there would be loads of folks interested to learn 'what their plants see'.

    BTW for anyone interested. I looked up the bulb and it runs around 6-7$ for a 4' tube. Well worth the much higher quality.

    Tony
    Is that a Nepenthes in your pocket or you just happy to see me?

  7. #15

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    I would love to be able to set up a nice comparitive study and present some publishable data describing the PAR of various T-12 avalible, but right now I don't foresee that happening. I did this comparison a few months ago and don't have all, or the exact, values infront of me. But if memory serves me correctly the GE Plant and Aquarium bulb was producing about 30 umol/m2/s (incase anyone is wondering, PAR is measured as the number of photosyntheticly active photons striking a unit area over some period time, that is why it is given in umol/m2/s). ESU's UVB and UVA (Desert Sun Bulb, I belive), along with a soft white bulb (I belive by Phillips), a Sunlight bulb (can't rember the exact name, but it comes in a yellow and orange package), and the standard Cool White by Sylvania (along with a few other bulbs I can't think of) were all pretty similar, producing between 50 and 70 umol/m2/s. The F40SP65 was producing around 100 umol/m2/s. Like I said before all the bulbs were the same age, but they were not right out of the box. So do not take these values as word of god as to what the bulb will do, just something to compare between bulbs (obviously a newer or older bulb will behave diferently).

    Tony I think you are still a little confused as to what color temp is. I had the same conceptual problems with it for the longest time. Trying to reconsile it being the color of the bulb, but not the "color" of light it produces (ie the spectrum). Even though there may be some lose correlate between the two, it is a common pitfall to think the color temp describes the spectral out put.

    Good call on looking up the price. I should have included that. The bulb is difficult to come by where I am at (Gainesville FL), where the only way I found to get them localy is to purchase a case of 30 (not going to happen). But every where else I have lived I have had no problem finding them.

    Enjoyed the conversation Tony,
    Jay

  8. #16
    drosera guy
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    Quote Originally Posted by [b
    Quote[/b] (jhupp @ Oct. 25 2004,2:35)]Tony I think you are still a little confused as to what color temp is. I had the same conceptual problems with it for the longest time. Trying to reconsile it being the color of the bulb, but not the "color" of light it produces (ie the spectrum). Even though there may be some lose correlate between the two, it is a common pitfall to think the color temp describes the spectral out put.
    The light colour in [K] is an indicator to show you how hot a perfect black body must be to produce the same spectrum as the lamp does. So check your physics book!

    Jan

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