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GulfCoastAquarian 02-05-2003 03:34 PM

If you haven't read this article yet, I highly encourage it. It is long and requires a bit of understanding of biology and physics, but you'll learn a lot from it.

A Comparison Between Light Sources Used in Planted Aquaria

This came from a discussion I was having with one of our newer members, collapse. He was wondering what impact lumens had on choosing a lighting system for plants. My intial response was that lumens are far more important than color temperature or CRI and should be a prime consideration when choosing a bulb for your planted tank. But then I re-read this article and fell across this passage:


Based on the Photosynthesis Action Spectrum (the wavelengths that plants are more sensitive to), light bulb manufacturers came up with fluorescent "plant bulbs". They basically emit most of their light in the wavelengths that are more efficient for photosynthesis, namely the red and blue ends of the visible spectrum. As expected, these light sources look dim to the human eye and consequently have poor lumen ratings. Also, their color temperature and CRI ratings have little, if any, meaning. After all, these bulbs were not designed to be "seen" by humans.
Obviously, not all humans like the pinkish glow these bulbs emit, but our plants sure do.
The popular GE Plant & Aquarium bulb is only rated at 1900 lumens, yet offers a PUR (photosynthetic useable radiation) of 20.9. A generic 4100K "cool white" bulb has a much higher lumens rating of 3050, but only offers 20.5uE/s of PUR.
Recently I switched to OSRAM/Sylvania's Gro-Lux bulbs (sold at Lowe's) and these bulbs have an even lower lumens rating at 1200, yet offer a PUR of 27.4!! In the ODNO thread, ridns replaced his 5000K Phillips T8 bulbs with these same bulbs from Lowe's and even though the total lumens output has decreased, his plants started pearling within 10 minutes! The high-CRI Phillips bulb he was using (Philips TL950 5000K CRI (98) F32T8/TL950) had a standard lumens rating of 2000, yet only offered a PUR of 8.9 uE/s! He was effectively increasing his photosynthetic useable radiation by over three times even though the apparent brightness of the bulbs decreased.

Ok, so if you're still with me, what am I trying to say? Basically this, don't think you've increased the amount of light your plants can use just because one bulb looks brighter than another.

Have fun!

GulfCoastAquarian 02-07-2003 01:30 PM

Well there are plenty of views on this thread but no comments so far! I'm going to keep it up top for a while just to make sure everyone gets a chance to see it. There has been so much discussion about bulb selection recently, I think this is important information for us to consider.

ridns 02-07-2003 01:38 PM

I don't know if I can attribute this to the P&A bulbs or not but; since changing to them my tank has pearled like crazy every day. Prior to this I was getting pretty discouraged because it didn't. I have also started the PMDD from Rex so this could also be the reason. What ever the cause, I hope it continues!
:bounce: :angel: :hehe:

GulfCoastAquarian 02-07-2003 01:51 PM

It is definitely possible that the Plantex triggered the pearling if you previously had a micronutrient deficiency, but the extreme difference in PAR between the high CRI Phillips TL950 bulb and the Gro-Lux bulb you switched to seemed to illustrate the point very well. To support this argument, would you be willing to switch back to the Phillips bulbs for a few days and then back to the Gro-Lux bulbs to see if pearling discontinues and resumes?

collapse 02-07-2003 03:45 PM

Last night I hooked up 2 commercial 2ft 2 light fixtures and put 4 of 20 watt standard glo lux bulbs in over my 26 gal bow front. I havent seen any drastic changes yet but the light was only on for maybe a hour.They really make the colors of the plants and the fish come out. I am curious to see what happens after a full 12 hours of use. Sam i notice on the packaging the bulb came in that it said the standard bulb was mainly for seeds and seedlings. Does that mean its got a higher output? What do you think that means?


ridns 02-07-2003 04:01 PM

Now why didn't I think of that ??? I'll do it tomorrow while I do the weekly water change. This should be interesting!
:bounce: :angel: :hehe:

GulfCoastAquarian 02-07-2003 05:26 PM

I'm not sure why they indicate for seeds and seedlings, but that is obviously in reference to terrestrial plants so I wouldn't worry about it. The standard Gro-Lux bulb is the one that was top on that list for regular fluorescent tubes. The Wide Spectrum looks a little bluer, and seems brighter, but only at the expense of some PAR.

GulfCoastAquarian 02-10-2003 01:34 PM

I hope I didn't cause too much confusion, but I moved Here4TheBeer's ODNO discussion to a new thread since it was getting pretty far off topic for this thread. :D

ridns 02-10-2003 02:05 PM

Sorry.... I posted the results of the above bulb test under ODNO......
:bounce: :angel: :hehe:

PhishNeslo 02-11-2003 01:35 AM

you are right on about some flourscent bulbs looking dim to the eye but still providing a bunch og energy to plants. GE makes two plant bulbs. the popular GE P&A bulb is usually a "wide spectrum" (it says so by the label on the bulb) version one that emits more visible light, but they have another "narrow spectrum" that looks really really dim. almost like a pinkish purple black-light.

one important thing to note though: while there is not a direct correlation between light intensity and photosynthesis (if the light is intense but at the wrong part of the spectrum), the more intense the light, the better it is at penetrating the water, so while the GE wide and narrow spectrum bulbs might grow plants equally well in air, the wide spectrum will be better at penetrating to the bottom of the tank

PhishNeslo 02-12-2003 10:35 PM

the bulb that was talked about above is mainly for seeds and seedlings because it wont make things flower or grow fruit. you need different light for that, like high pressure sodium (which emits energy in a part of the spectrum that makes plants think it is time to grow fruit that is also really good for photosynthesis)

PhishNeslo 02-12-2003 10:36 PM

grow lux bulbs are good, but i have had lots of success with "Ott-lite" they are really bright for t-8s, and have a really high PAR

m.lemay 02-13-2003 02:58 AM

I have 55 watt PCs on my tank. I'm currently shopping for some High PUR bulbs in the 55watt PC configuration. Is there any PUR data out there for these 55 watt bulbs. Do they make the sylvania GRO-lux in a 55wattPC bulb and who sells them?

GulfCoastAquarian 02-13-2003 12:49 PM

I haven't ever seen any PUR specs on PC bulbs, other than the Sylvania 55w Dulux bulbs that are only available in Europe. Pet Supply Liquidator has some Plant Grow bulbs that are 50/50 tubes like reefers use, but instead of half actinic / half 10,000k, it is half red / half 6700K. I'm dying to try them out, but they are only available in straight pin (not square pin Panasonic) configuration.

m.lemay 02-13-2003 09:05 PM

9325K 55 watt
These are the bulbs I'm using now in my All-Glass fixture. I like them a lot and they seem to have the wavelength peaks in the right neighborhood.

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