Aquarium Light Project

Hello, this would be my first post.

I've ordered a cree XR-E 7090 and a 12V DC input 700mA output driver for an aquarium light project. The aquarium is a rather small 3L tank, and having read the data sheets, I believe the light intensity and wavelengths are suitable for the plant's needs.

I'm going to drive the LED with AA cells, and for 12V I would need eight cells. I was wondering if it is possible to mod the driver, so that the input would be 4.5V (3 AA cells).

And as an alternative, would it be possible to drive the LED with 3 AA cells and a suitable resistor? Moreover, would using zinc-carbon cells be alright?

why dont you just use a mains electricity transformer instead??

Modding the driver is very difficult and complex.

And it's not recommended to drive LED with AA cells and a resistor, you know LED is a semiconductor device and voltage sensitive, so using simply a resistor may cause overrun and shorten the lifetime of LEDs. As far as I know, all LED manufacturers recommended to drive them with a current-restricting circuit at least.

Thank you for your replies.

fluff34567,
I'm trying to keep my desk neat and tidy, so would prefer a cable-free set up.

fineday,
I understand the overrun problem with only a resistor. However, would it be alright if I supply a voltage slightly below the typical voltage, say 3.65V? As rated on the website I ordered the LED from, The DC forward voltage is 3.3V for 350mA, and 3.75V for 700mA.

Are you trying to mod on of those plastic beta style tanks?
But driving the LED's at 3.65 volts will put them somewhere near 700 mA but not quite, if you bought a 12 volt unit you will need to run it at the full 12 volts, and the requires 8 cells.

Hello winsonli, a very warm welcome to CPF, i hope you enjoy your stay with us !!
........my first thoughts are that it would be a relatively expensive proposition to run on AA batteries, cheap (zinc/carbon) batteries dont tend to last very long,
also even if you could succesfully mod the driver to run at a lower voltage the runtime would be vastly shorter so there would be no real gain to the mod.
go with the 12v but consider recargeables, they work out cheaper and they are kinder to the environment

65535,
Well its a glass one. I guess driving them near but under 700mA should be fine, and it would generate less heat also.

HEY_HEY_ITS_HENDO,
Thanks.
I don't have much knowledge in electronics and there's one thing I don't understand. Why would a decreased voltage give a shorter runtime? Say, if 8 cells of 3200mAh are in series, shouldn't the capacity be the same with 3 cells of 3200mAh in series?

How about using 3 rechargeables with a resistor? If I keep the voltage under the typical voltage, would there be problems with this method?

winsonli said:

However, would it be alright if I supply a voltage slightly below the typical voltage, say 3.65V? As rated on the website I ordered the LED from, The DC forward voltage is 3.3V for 350mA, and 3.75V for 700mA.

Click to expand...

It will be OK if you can ensure that voltage, but I think it'll be difficult to keep that voltage exactily only by resistors.

Or, you can just use a resistor a little bigger than what u want, for example to restric the current to 500mA. Just lost some brightness but be safe. LED's not cheap

I guess driving them near but under 700mA should be fine, and it would generate less heat also.


What if he mounted them *in* the water, and let the tank cool them?

I grow corals useing a natural ecosystem approach that involves growing a macroalgae in the refugium tanks below the displays. I have quite a bit of experience in the relationships between wavelegnth, PAR and getting useful light to the plant.

The spike you see in many white LED's around 460nm falls between the range that qualifies as PAR, yet any experienced aquarist will tell you corals and macroalgae does not make use of it. You are likely carbon source growth limited rather than light limited for your tank. Something to cause surface turbulance to improve gas exchange would likely be a bigger improvment in growth than mounting an LED above the tank. Also, I think driving this with batteries is a very foolish option, but if you must, you should know that a series of flashes of intense light to trigger photo-events to begin followed by weak/ambient lighting can result in equal or even improved growth VS constant light.

Also, photoperiod will be crucial, as for some species leaving a light on 24-7 will cause death from failure to complete the day/night cycle that is required to complete "photo-feeding" cycles.

Please give explicit details and I will be better suited to advise you.

Seems there is a similar project here.

fineday,
I just found out that rechargeables are of 1.2V, so 3 of them would give 3.6V without any resistors. So when the voltage drops I'll just lose some brightness and changing the rechargeables would do.

Ken_McE,
The aquatic plants I grow would require temperatures around 25 degrees C, so in the summer it might be too hot. In fact, I would need some kind of cooling fan to cool the tank down. Perhaps I could cool down both the water and the LED with it.

liveforphysics,
Thanks for your professional advice. I'm growing freshwater plants and I think there's a bit difference. The species I grow demand high light intensity and CO2 concentration. So professional hobbyists actually inject CO2 into the water from a pressurized container. And for lights, they use halogen lamp. But as a cheaper alternative, I supply CO2 by letting yeast carry out anaerobic respiration in a container. This method is widely used by a number of freshwater hobbyist with a tight budget.

With an ample supply of CO2, the limiting factor would be light intensity. I believe flashing the LED would be a great idea to improve plant growth and prolong battery runtime. Could you suggest the time interval for the flash?

Also, shouldn't the second stage be light independent? Would I have to give a weak LED light, or the very weak ambient light will be ok?

In this case, the Cree LED would only be on when I'm at my desk, for illuminating purposes. For the plant photosynthesis, I would flash blue and red LEDs on it. It would be the most energy efficient this way.

Winsonli- I need to know the species you are growing and I can ask a fellow freshplanted tank expert as to lighting wavelegnth recomendations. I specialize in Marine varietys only.

I often see sugar/yeast CO2 sources often used with planted tanks. I use a yeast/sugar CO2 feed to locally drop pH in my Calcium reactor to create an effulent rich in Ca and CO3 for the corals. However, you may find that perticularly in an inside/office enviroment that increased surface turbulance can create higher available Carbonic acid than a low rate CO2 generator. You will also note a trend between near surface(near because surface speed is always zero) water speeds at the photo-feeding tissue will increase the levels of light the plant can tolerate, as well as the efficiency at which it makes use of the light.

I know temperature regulation on a 3L tank would be a real challenge in the summer, and carefully designed power efficient flow could aid in the cooling. The little 17gal coral reef I setup at work had a hell of a time keeping cool even while the enviroment stays roughly the same temp 24-7. Could be related to that 250w MH bulb sitting above it... Or the ~700GPH pump circulateing water through its 2 below mounted refugiums...

Anyways, get me some species info and I will get you some expert info from my buddy on optimal wavelegnths of light for your intended species. Sadly, I do not belive that 460nm is useful for any photofeeders, and it happens to be the bulk of most LEDs.

Best Wishes to you!
-Luke

I just noticed you said the Cree would be only for viewing purposes, in which case, use whatever and go for it! Can't hurt anything if your goal is just for looking

best wishes!

Luke,

Thanks for your input.

As I know, the two common photopigments absorb wavelengths of around 460nm(blue) and 625nm(red). I was wondering if it is possible to choose the right wavelengths and intensity so that the plants thrive and algae growth is controlled.

Blue light penetrates deeper in water. So brown algae is found in deep waters and blue green algae is found in shallow waters. As for plants, I guess corals require blue lights and freshwater plants would prefer red. I'm not sure about this though.

The species I grow are Eleocharis ''parvula'' and Hemianthus callitrichoides ''Cuba''. It would be the best if you could ask your buddy for an optimal wavelength, so to choose a single-coloured LED for the growing/photosynthetic purpose. Thanks a lot!

Thanks for the species names I will get back to you on ideal lighting as soon as I get the chance to ask my buddy. Could you show me what causes you to belive 460nm is useful? I ask because 460nm is a very common wavelegnth to generate via LED, florecent, or MH, and so many aquarium bulbs use that phosphor as the main wavelegnth peak to raise color temperature. Its been found to cause effectively no growth in corals and cause death from starvation in macroalgaes(when its the only available light), even at extremely high light levels. Still so many brands try to market/claim there bulbs peak at 460nm because its useful/good light rather than saying that they peak at 460nm because its the cheapest common efficient phosphor available to drop color temp on bulbs for the purpose of pleasing the consumers eyes alone. Now, 415-430nm light looks much less attractive to the users eyes, only is efficient enough to make a small fraction of the light output, yet when grows corals like weeds, and when combined with some ~670nm phosphors, grows macroalgaes at very high rates. Now, like I mentioned before, I am definately specialized towards marine photofeeders, and freshwater may have entirely different needs.

I will get back to you via-PM as soon as I am able to contact my buddy.

Best Wishes

Thanks

While I was doing research for this project, I came up with the webpage ledgrowlights.com which is about terristrial plant growing with LED lights. They have this graph under their "advantages" section:



The graph shows a peak at around 430nm and 460nm, and that's why I believed 460nm is one of the effective wavelengths (assuming that terrestrial plants have similar photosynthetic mechanisms to freshwater plants).

I did another research on wiki just now and found out that only chlorophyll a is universal in all plants. Below is the graph on wiki:


So assuming that aquatic plants and corals only have chlorophyll a, wavelengths of 415nm to 430nm should be optimum, just as you said. I might be wrong if the two species don't have chlorophyll b. But for certain providing wavelengths of 415nm to 430nm would be utilized by the plant.

For plants honestly a MH arc lamp or full spectrum halogen would be best, but target wavelength LED lighting cna be used, make sure you can find good lights.

65535- MH is definately NOT suited towards a 3L tank. Halogen is extremely poorly suited towards this application. MH in a phosphor coated plasma chamber are used often with larger aquaria, but arc lamps would cause imeadiate tank crashing due to UV light sterilizing the life supporting nitrifying bacteria.


Your chart is quite excellent, and shows what I am describing much better than I could phrase it. ClorB is something that I personally do not encounter in my marine photofeeders. That leaves 670nm and 415-430nm light to be all that remains to be useful (at least for marine species). Again, I am just dealing with zooanthellae dinoflagellates and macroalgae species, so I dont even deal with any plants, which could contain clorB.

You could do some fairly simple experiments with a partition in the tank and one side getting pumped with the peak useful wavelegnths for clorA and one side getting the peak useful wavelegnths of clorB and see which side has improved growth (or survives).

Its good to see another sharp person on this board. NeedleNHaystack