LED Tank Lighting Experiment with 1st look at results...

This is a continuation of a discussion on using low wattage LED lighting for fish tanks. I started a new thread as this has moved from a general thread discussion to a more specific discussion with LED details and may be added to by other members with their LED experiences.

A few days ago, I caught a few comments in the forum on using LEDs for fish tanks and the discussion was mixed. High prices, potential unrealized longevity,color temperature and possible plant benefits.

During the discussion, I had been considering buying a string of white waterproof LED lights from a Chinese company I have done business with before. As they just recently started a US warehouse delivery time was cut from several weeks to a few days. The company is called Deal Extreame.com and the item I bought was this:

http://www.dealextre...c-12v-900116211

At 14.95 USD and being waterproof, I thought that this was a low enough price to go ahead and buy one unit and experiment with it to see what potential benefits might be obtained with it's uses. I will say up front that I have no association with this company other than purchasing from them from time to time on low cost items. So far, all the items have been as advertized and in working condition. I take the time to read the comments from other buyers and sometimes the quality and longevity is reported as less than desired. As this is a Chinese company I believe you get what you pay for and sometimes you can be lucky and sometimes not. Cost is the factor in giving something a try for me so let any buyer be warned.

The unit came boxed with no problems. The unit is stated at 4.5 watts and contains 30 LEDs. It runs from a 12 volt power supply which was not included at this price. This was not a problem as I had several cheap 12 volt wall plug type power supplies laying around. The wall plug power supply I used is rated at: input 110/220v; output 12 volts DC at 0.5 amps. It fired up the lights just fine without issues.

As I just got the LEDs today, so I thought I would give it a try on the tank and take some pictures. I used several positions and simply used tape to fasten the LED light strip. I set the camera on a tripod and took a few pictures and saw that the auto programmable aperture/shuttersetting the camera was set on was compensating for the light differences so would not be appropriate to show any actual visual differences between locations and usage in these pictures. I used a wide angle Nikon lens with the camera set on a tripod in front of the aquarium at about 3 feet away. I switched the camera to manual settings and set as standard a setting of F6.7 for 1 second. All pictures presented here are taken using this one setting. I imported the shots from the camera into Photoshop and cropped them and re-sized the pictures from 4194x2076 to 1024x510 to reduce the file size. There was no digital image enhancement performed.

The LED lights:



1. The standard: Here is the first picture. It is my 55 gallon aquarium as it normally is with just the two top florescent bulbs - ON. I have already taped the LEDs to the top front glass but they are OFF for this shot. Florescent ON and LED OFF.



2. LED taped to the outside of the aquarium' s front - top of glass - facing directly straight in. Florescent ON and LED ON.



3. LED taped to outside of the aquarium's front glass - angled down at about a 60 degree angle(held in place using tape). Florescent ON and LED ON.



4. LED taped to underside of plastic lids of tank top units with LEDs facing directly down to the gravel. Florescent ON and LED ON.



5. Florescent lights removed and LEDs placed face down on glass where Fluorescents had previously sat - in the same position. Black plastic covers placed back on top so LED light only goes into aquarium - the same as for the fluorescents when they were in place. No Florescent light and LED = ON. It appears to me that the LEDs might be sufficient replacement for the florescent when comparing intensity only.



Sorry, but I don't have light meter so my further comments here are from my visual observations only. Your guess is as good as mine here. I have to say that where I was initially not holding my breath for any good results it appears that these LED's give off a good deal of light. Possible as much as the fluorescents by themselves and maybe a little bit more. The LED color is visibly cooler than the fluorescent lights.

I had originally intended to use the light to simply enhance the ability to see the fish in their colors better. I don't see a big difference at this time with the lights in these temporary positions, however it is apparent that there is additional light in the tank as you can see intensity increases in certain locations and added light glare from the back of the tank off the wall and glass itself. Maybe if they were taped to the front of the glass mid way down this might be achieved but I don't want to put the light there for esthetic reasons.

As for benefitting the plants; the light output from the LED lights is visibly considerable and would probably be a benefit for the plants in the tank as well. I can not be for certain about this without installing the LEDs and watching the plant growth.

This was a low cost experiment and I think it has potential. Hope this provides someone with sufficient information to try experimenting with LEDs themselves.

I have my fish cam running tonight and I have decided to leave the LEDs under the florescent covers with both the LED and florescent lights on during the day. I will check on plant growth with this setup for a few weeks.

http://localhost:808...ndex.html?cam=0


Usil

Edited by Usil, 22 September 2011 - 06:00 PM.

Sorry, I provided wrong IP address for Aquarium WEB cam.

Here is correct link: http://71.170.193.21...ndex.html?cam=0

Google Chrome times out sometime too quickly to make the connection so use IE 9. Don't know about Firefox or other browsers.


Usil

As for benefitting the plants; the light output from the LED lights is visibly considerable and would probably be a benefit for the plants in the tank as well. I can not be for certain about this without installing the LEDs and watching the plant growth.

Do you know the spectrum of the light that comes out of the LEDs? If there are peaks in the 400-500 and 600-700 nanometer portion of the spectrum, then chlorophyll would be able to utilize the energy.
Chlorophyl absorption spectrum: http://www.chm.bris....l/chloroabs.gif Source: http://www.chm.bris....lorophyll_h.htm

Edit:
I have been googling ways to find out the emission spectrum of a bulb yourself, and it looks like if you just take the light, turn it on inside a box with only a narrow slit for the light to escape from, and then direct that light beam through a prism, the result will be the spectrum. Schematic: http://www.800mainst...prism_light.gif
If you see lots of vertical lines colored purple/blue and red, then it's a good light for the plants in your tank.

Edited by EricaWieser, 22 September 2011 - 08:47 PM.

I have no way to tell what the exact spectrum is but as it is white light suspect it has some in these frequencies. It does not have the appearance of having a lot of blue or red in any particular abundance but looks pretty even. But this is just my visual observation. I don't have a prism either so can not perform this experiment. If I can find a prism somewhere I will give it a try.

Usil

Edited by Usil, 22 September 2011 - 08:53 PM.

If I can find a prism somewhere I will give it a try.

You can use water. Link: http://www.sciencefa...ough-water.html

At 14.95 USD and being waterproof, I thought that this was a low enough price to go ahead and buy one unit and experiment with it to see what potential benefits might be obtained with it's uses. <snip snip> The unit is stated at 4.5 watts and contains 30 LEDs. It runs from a 12 volt power supply which was not included at this price. This was not a problem as I had several cheap 12 volt wall plug type power supplies laying around. The wall plug power supply I used is rated at: input 110/220v; output 12 volts DC at 0.5 amps. It fired up the lights just fine without issues.

Very interesting. The coloration in the LED-only picture is a bit different from the original fluorescents ... what kind of bulbs / what watteage? ... but to my amateur eye looks to be producing pretty decent illumination in your 55. The fish under the right-side wood isn't out far enough so that its colors are clear, keen to hear how you think the fish colors look under the LEDs compared to your regular lights.

It's also worth noting that not everyone is trying to grow real, light-loving, plants. In which case, only 4.5w is REALLY attractive from both an electricity cost and a cooling perspective.

And I can't clearly make it out from the picture of the string on the carpet ... these are focused-downward "bulbs" that don't need any kind of reflector, so that's even more cost savings for an installation ?

Can you daisy-chain these particular light-sets so one power-supply can handle two or three sets ? If so, that (and the fact they're waterproof) would make them very functional for lighting racks of tanks in a fish-room.

Thanks for sharing ! Sorry for all the questions, it's not really an interrogation even if it might feel like one, but you do have me intrigued.

Very interesting. The coloration in the LED-only picture is a bit differentfrom the original fluorescents ... what kind of bulbs / what wattage?

Their are two original fluorescents light hood fixtures above my tank. These fixtures are the standard black plastic removable ones that fit the top tank cover. Each fixture houses an 18 inch long, 15 watt florescent bulb identified with these markings: Perfecto Manufacturing - Perfect-A-Lamp F15TB.

In a cursory brief search, I have tried to get further information on these florescent lamps but it is difficult to be sure exactly what they produce. I saw a reference where someone contacted the company and that the spectrum information was not provided to him. I suspect that these bulbs are sourced based on availability and costs and are subject to frequent change making it difficult to provide a standard from which to make a comparison. This leads us back to testing them ourselves to be sure if we have specifications we want to meet. Gro-lux bulbs may provide a more consistent standard.

The reviewer referred to a comparison chart but I was notable to find it. He stated "If this curve is reliable, this bulb is basicaly a gro-lux bulb. The spectrum looks similar to the Osram/Sylvania Gro-Lux, but with wider emission lines (due tospectrophotometer resolution ?) and somewhat less red emission. http://fins.actwin.c...3/msg00635.html

...but to my amateur eye looks to be producing pretty decent illumination in your 55. The fish under the right-side wood isn't out far enough so that its colorsare clear, keen to hear how you think the fish colors look under the LEDscompared to your regular lights.

Yes, I agree. The 4.5watt LED lamp strip is producing impressive light compared to the 30 watts from the two florescent bulbs. This one 4.5 watt strip is sufficient to replace the two florescent bulbs for this tank. They look comparable to me with just a little less red in it. Certainly, not a sickly white but a very clear neutral white. The fish look very good under them so I am satisfied. I believe they can also grow plants. We shall see.

One of the problems with LED lamps is the variability of the whites they produce. I have been looking at regular LED bulbs for regular fixtures for a year and reading all the consumer reviews. There is an astounding number of different whites available and again, based on sourcing and costs are probably not standardized. To me the LED lamp is still a work-in-progress but there are benefits to be had if we decide to pursue and do our homework.

It's also worth noting that not everyone is trying to grow real, light-loving, plants. In which case, only 4.5w is REALLY attractive from both an electricity cost and a cooling perspective.

4.5 watts from the LED lamp strip compared to 30 watts of fluorescents and producing even or more than even whites is impressive. It surprised me. The lamps and small power supply are running cool after 2 hours of operation. When I went to get the information off the florescent bulbs I had to be careful to stay away from the hot ends.

And I can't clearly make it out from the picture of the string on the carpet ... these are focused-downward"bulbs" that don't need any kind of reflector, so that's even morecost savings for an installation?

The LEDs are embedded in a plastic strip. I suppose that each LED is on a small circuit tab that provided a stable base and reflection point behind the LED. No additional reflector is needed. You can not daisy chain these. But I see no reason not being able to add several LED strips handled by a slightly bigger power supply. I could easily lay three or 4 strips on top of the glass under the fluorescents if you really wanted massive light for the tank. The fact that they are waterproof makes them perfect for using around an aquarium. A 12 volt power supply could be picked up at Radio Shack if you don't have an extra one around.


Usil

Edited by Usil, 22 September 2011 - 11:19 PM.

Do you know the spectrum of the light that comes out of the LEDs? If there are peaks in the 400-500 and 600-700 nanometer portion of the spectrum, then chlorophyll would be able to utilize the energy.
Chlorophyl absorption spectrum: http://www.chm.bris....l/chloroabs.gif Source: http://www.chm.bris....lorophyll_h.htm

I went and looked up which semiconductors have emission in that part of the spectrum. That way, instead of having to do a test to see what the emission spectrum of the LED is, you could know simply look at the ingredients to tell if the LED emits light at the right wavelength for plants. Here's the info, straight from wikipedia.

Red:
Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium(III) phosphide (GaP)

Blue:
Zinc selenide (ZnSe)
Indium gallium nitride (InGaN)
Silicon carbide (SiC) as substrate
Silicon (Si) as substrate – (under development)

Source: http://en.wikipedia...._emitting_diode

So if your LED has an ingredients list on it of which p and n dopants it uses, and if you can match them to the ones listed above, then the light probably emits a peak in the region of the spectrum that plants use for energy. But there's a chance these LEDs are phosphor coated, which means you'd still need to do the test with the splitting of the spectrum to see which wavelength of lines you'd get.

I apologize if I'm being sort of annoying, but since all of my tanks contain live, growing plants, an aquarium light doesn't have any value to me unless it can be used as an energy source by those plants.

Edited by EricaWieser, 23 September 2011 - 03:11 PM.

Usil,

Boy, am I glad you retired. You post some of the most interesting stuff on this board.

I am with Doug_Dame; for me cost and efficiency is important as long as I can find some plants that will work in the environment that I create. So far, so good.

Keep up the good work.

'Erica' -Unfortunately there was nothing else in the box including a description sheet that could help us here. I understand you would like some specifics and I would love to be able to give them to you. Empirically,we will have to look at how we might be able to do that and I am considering some options since further study can be a benefit to all of us. So, I am not giving up on this.

Right now,all I can do is just turn them on and wait and see. I have ordered a second unit and will be putting one on the right side and one on the left (will wrap them in a U-shape to fit under each hood) to replace entirely the florescent bulbs currently used (will turn them off). 'Mich' - The ability to exchange 9 watts for 30 watts is worth it to me too, to give this a try.

I am going to buy a prism. I should be able to find one somewhere cheap on the web. When I get one, I will set up a standard experiment to see and photograph the spectrum spread and post the results. I just realized I do have a light meter - my Seconic L-508 Zoom Master I bought for my camera and for which in the 20 years I have had it, I have never used. I will have to review the capabilities and see if this might be of use to make some sort of usable base measurements of incidence light intensity that can be of use.


Usil

Edited by Usil, 23 September 2011 - 07:15 PM.

It might be useful to establish a written knowledge base on the subject of light requirements for growing plants in an Aquarium. I have been collecting references and there is a mass of information that I need to sort through and condense. Give me a couple of days to do this and I will organize it and post it in this thread. This should establish a base for comparison and standardize our discussion and selection process.

In addition, instead of a prism, I am going to purchase a holographic diffraction grating to use in comparing and describing the LED and Florescent bulbs I have on my aquarium. I suggest those interested in this thread to purchase the same 'inexpensive' grating and perform similar tests on their aquarium lights. In this way, we can accumulate data and discuss these comparisons.

The unit I will purchase is this one: http://www.arborsci....Grating-45.aspx at $USD 3.00.

Just read my instruction manual for my Sekonic Light meter. I am able to take EV readings and compare them to a chart to read off the lux or ft candles provided by the source. So, I will set up a dry test for my LED and florescent bulbs using the distance from the top of the aquarium to the gravel bed. I guess I could put the whole meter in a plastic bag and actually lower it into the aquarium and try to take a reading under water at the level of the gravel too.


Usil

Edited by Usil, 23 September 2011 - 10:26 PM.

for me cost and efficiency is important as long as I can find some plants that will work in the environment that I create.

And I am with MichiJim.

Regardless of my substrate choices, there are four kinds of plants that I consistently do well with (the others, not so much): Java Fern, Java Moss, Artificial, and None. All do well under moderate light conditions and probably would do decently under these LED lights too.

(I'm not proud of it, I'm just sayin'.)

Ok. I set my light meter to read EV values at the gravel level of the aquarium. As a quick and dirty test I set the meter on the aquarium table with the light sensor up to the glass pointed at a rock at the level of the gravel at the bottom of the aquarium. I took readings for the Florescent bulb only on; then the LED only on and finally with both on. I then calculated the Lux and FC values from these EV readings. I repeated the tests several times and made sure that the light meter was pointing exactly to the same point on each test.

I would have used a table conversion to get these values but the resolution of the various tables I found was insufficient for the values I was reading from the light meter so I calculated these values based on formulation: lux=2.5*2EV and FC=lux/10.7639. I don't have a scientific calculator to get the lux value so I used WolframAlpha ( http://www.wolframalpha.com/) to do the calculation for me. Below are the results:

Light source-----Lux----------FC
-----------------------------------------
Florescent-------6.16-------0.572
LED---------------4.67-------0.434
Flor+LED-------10.72-------0.996

So, while visually they look similar there is a small difference. I find that the results are remarkable when comparing the wattage of the tested lamps. I think this test is sufficient for a dry-test comparison combining reflected light at the level of the gravel in the aquarium through the glass. I need to see if I can get a truly water proof bag to try this test fully under water.

Usil

Edited by Usil, 23 September 2011 - 11:26 PM.

In addition, instead of a prism, I am going to purchase a holographic diffraction grating to use in comparing and describing the LED and Florescent bulbs I have on my aquarium. I suggest those interested in this thread to purchase the same 'inexpensive' grating and perform similar tests on their aquarium lights. In this way, we can accumulate data and discuss these comparisons.

The unit I will purchase is this one: http://www.arborsci....Grating-45.aspx at $USD 3.00.

That's neat. I wish it had occurred to me to think of diffraction gratings when I was trying to come up with alternatives to prisms; that $3 model seems excellent. I hope that the small size of it doesn't get in the way of your light splitting experiment. Maybe a couple sheets of black cardboard paper glued together for thickness with a hole cut out in the middle and this diffraction grating placed in, maybe that might work. Thank you for taking such efforts to answer my question

Edited by EricaWieser, 24 September 2011 - 08:53 AM.

No problem. Winter is coming and I was looking for a good project to keep me busy.


Usil

Light source-----Lux----------FC
-----------------------------------------
Florescent-------6.16-------0.572
LED---------------4.67-------0.434
Flor+LED-------10.72-------0.996

It's interesting to me that you're using the Lux unit of measurement instead of lumens. I had to go look up what a lux was, and it seems like it's one lumen per square meter. Is there a reason you're using luxes instead of lumens? Has your calculation used the footprint of your aquarium or been normalized to a square meter in any way? I'm just suspicious that your answer is inaccurate because it doesn't correlate with the following chart from wikipedia:

Illuminance........................Example
10−4 lux.................................Total starlight, overcast sky[2]
0.002 lux.................................Moonless clear night sky with airglow[2]
0.01 lux..................................Quarter moon
0.27 lux..................................Full moon on a clear night[2][3]
1 lux......................................Full moon overhead at tropical latitudes[4]
3.4 lux...................................Dark limit of civil twilight under a clear sky[5]
50 lux....................................Family living room[6]
80 lux....................................Hallway/toilet[7][8]
100 lux...................................Very dark overcast day[2]
320–500 lux...........................Office lighting[9][10][11]
400 lux..................................Sunrise or sunset on a clear day.
1,000 lux...............................Overcast day;[2] typical TV studio lighting
10,000–25,000 lux.................Full daylight (not direct sun)[2]
32,000–130,000 lux...............Direct sunlight

So that's why I think the lux unit here must be being used inappropriately; according to that chart your approximately five lux is about as illuminated as twilight under a clear sky. It's ten times darker than the family living room's lighting, and that can't be right; the tank looks very bright.

I have put together a list of resources that should allow us to understand what it is we are trying to do. Briefly stated we want -

• A basic understand of the light requirements for growing aquarium plants
• To develop a cheap methodology of measuring and comparing the output of our aquarium light sources that can be used by NANFA members across the entire membership across NA.
• To understand the differences and benefits between the different types of Aquarium lights we have or would like to use (output, energy required, correct spectra, efficiency, longevity, etc...)
• To understand if LED aquarium lighting will provide aquariums with the right light requirements (or superior) to provide good growth, with economic benefits.
• To determine if inexpensive Chinese LED lights might provide for this benefit

I could spend a lot of time summarizing all the available information and have a lengthy post or I could organize what is available on plant growth and aquariums into a reference for those wanting to follow this discussion. Because I am lazy I chose the latter. I will add comments at certain points and this is an open discussion so anyone can chime in and add to the discussion with questions or comments. In some cases the references are from vendors which do provide some good information in this review.

Good Discussion on Plant Light Needs:
http://forum.grassci...tosythesis.html
http://retirees.uwat...hids/light.html
http://5e.plantphys....hapter.php?ch=7
http://extension.mis...ub.aspx?P=G6515

Spectrum of Florescent light:
http://www.bealecorn...trum/index.html

Grow-Lux Bulb Lighting:



Understanding Light Energy for Plant Growth (Biological Action Spectra):
http://www.biocontrols.com/aero65.htm http://www.photobiol...nfo/Gorton.html










Aquarium Lighting:
http://www.americana...m_Lighting.html

Action and Absorption Spectra:
http://users.rcn.com...onSpectrum.html

Benefits of LED GrowLights:
http://ultraledlight..._advantages.htm
http://www.lumigrow....growing-plants/

Multi-color FullSpectrum LED Grow Light:
http://ultraledlight..._grow_light.htm

LED Aquarium Lights:
http://americanaquar.../LEDLights.html http://www.ledaquari...W-T5-12-G2.html

LED Light - Normal room light:
http://bulbtronics.c...CookieSupport=1

LED Light Products:
http://www.ledaquari...uarium-led.html
http://www.dealextre...c-12v-900116211

Making measurements. As I don't think we are a group that can be considered rich (no offence to the rich) I think that how we proceed should be economical and universal enough so that any one of us can proceed and provide data for a joint comparison. This should be done with what we have on hand or can easily and economically purchase.

I have found that a photographic light meter which is capable of reading incidence light and provide EV readings is a good starting point in allowing us to measure the output of the lights we have. EV (Exposure value) can be directly converted to LUX and Foot Candle values. These values, while not perfect for measuring exactly the light requirements that plants need (which would move us into costs far exceeding what any of us would like to spend), they can provide an overall general review of total light received by the plants in the environment we are using. At least this provides us a starting point for light comparisons. We will have to use other means to include actually trying the lamps to see if there are real plant benefits. If others pursue this we can create a table of the data of the lights we are using.

Metrics:
EV can be converted to Lux values through the following formula. I have seen the constant 2.5and 2.6 used in the Lux calculation and I chose to use 2.5. As long as we all use the same formula we can standardize our results.

Lux = 2.5 * 2^EV
Foot Candles (FC) = Lux/10.7639

EV indicates a combination of camera settings rather than a photometric quantity of light exposure. Common EV ratings for various settings include:

Full sunlight - 15
Bright cloudy - 13
Heavy overcast - 12
Sunset - 12
Mall shopping areas - 8 - 11
Offices - 7 - 8
Home interiors - 5 - 7

The EV light values I measured at the bottom of my aquariumwere between 0.9 and 2.1 (as measured from the outside glass) depending on which lights were on. I need to get or make a waterproof housing/baggie to do this from actually inside the aquarium so I can measure the light downward hitting the bottom instead of light reflecting off a rock as measured from the outside of the tank). I suppose that if anyone is really inquisitive they can take what we are doing to the field and measure the light received in a pond or creek.

EV is measured based to a standard ISO 100 film speed through a light meter. A result of this provides a standard from which we can calculate luminance. Luminance is what we measure off of the surface that has light hitting it. Luminance is also considered the human perception of brightness or how bright we perceive the light is reflected off of a surface. Lux is the value expressing luminous power per area. Foot Candle (FC) is a value commonly used to express adequate lighting levels. I would suppose that Lux is sufficient for our needs in a table but I show both.

So, in a round about way, we can use a standard camera lightmeter measuring EV to begin the experiment of measuring light and end up with a value that we can use to compare our aquarium light sources. As a lot of us seem to be into photography a light meter might already be owned by many of us. Or this Lux meter with LCD display from Amazon ( http://www.amazon.co...y/dp/B000JWUT6O)can be had for 15 bucks.

Light Spectra:
The other important part this project is relating all of this to the spectra used by the plants. For this I have chosen to use a holographic diffraction grating. Here we move into a non measuring area where we will have to be creative to get usable results we can compare. I have not done this buy I envision that the HDG will provide a visible spread of light on a surface. This spread of light should be able to be photographed. And the photo image should be comparable to standard diffraction patterns for sunlight and lamp bulbs all of which we should be able to find on the internet.

Photographing the light diffraction pattern, cropping the image and pasting it into comparison shots of other diffraction patterns is not perfect nor provide measurable results but it does provide a visible basis for comparison that should still be useful to us.

The combination of these methods should provide sufficient data for discussion so that ratings can be reviewed for our existing lights in our existing tanks and future lighting purchases. I would be interested if others actually go beyond this project and do trials of plant growth using the different types of light. Perhaps choose one or several plants (low light plants, mid light plants and difficult to grow plants) as a standard and set up separate tanks with daily visual and actual measurements. After all, winter is coming and surely some of here would like to fill those long cold winter eves with some fun exploring our hobby.


Usil

Edited by Usil, 24 September 2011 - 09:50 AM.

We can add lumen to a table.

http://www.ledrise.c...ent.php?coID=19


Usil

The T8 spectrum posted above is just one spectrum from one T8 bulb. Each bulb design can have an extremely different spectrum, with some designed to be office white, some full spectrum, and some specifically designed with peaks in the red and blue to grow plants.

Since we're sharing what lights we use, I'll tell you about my current setup. I don't have a way to split the light into its spectrum, but I do know from over a year of using these bulbs that aquarium plants love them. Every one of the dozen or so species I've put under them has grown very well. It would be inexpensive for other NANFA members to use this setup and be able to grow aquarium plants if they so desired.

The bulbs I use are $8 for two bulbs at Home Depot. They are Lithonia 32 watt, four foot long T8 fluorescent bulbs, which fit into a 4 foot shop light that costs $20. It is a very convenient light for aquariums, being exactly the four feet in length that a 55 gallon fish tank is. Here is a photo of the light on my tank: http://img.photobuck...imiru/039-1.jpg If you buy two, they cover the 55 gallon tank's top so no fish can jump out.

Link to light fixture: http://www.homedepot...catalogId=10053
"Lithonia Lighting All Weather 4 Ft. 2 Light T8 Fluorescent Unit Shop light"

Link to bulbs:
These bulbs cost about $6 to $8 for two (the price on the link is for a 10 pack). I replace mine about once or twice a year.
1. http://www.homedepot...catalogId=10053 "Philips 32-Watt 4 ft. T8 Daylight Deluxe Linear ALTO Fluorescent Light Bulbs" 2,750 lumens, 6500 K, 24,000 hours of life
2. http://www.homedepot...=1&ddkey=Search "Philips 32-Watt Neutral Full Spectrum Linear Fluorescent Light Bulb" 2850 lumens, 5000 K, 20,000 hours of life.

There are like a dozen different 32 watt T8 bulbs to choose from, but both of those above work. Avoid any with less than 5000 K; they're yellow and they look icky in my opinion. For a white-white color, you want 5,000 K and above. Here's an image from wikipedia that demonstrates what I'm talking about: http://en.wikipedia....-comparison.png

Bulbs usually use lumens, not lux, as a measurement of their brightness. I'm not sure what these bulbs' light output is in lux. Lux seems an odd way to measure things since it is lumens/square meter.

Edited by EricaWieser, 24 September 2011 - 10:05 AM.

Usil, I'm getting a 'page not found' message when I click on most of your links. It then directs me to a yahoo search.

I wish I had time to run parallel experiments with you on this. I am watching closely though as I'm sure a lot of others are too. Your efforts are quite appreciated.

Steve.