# Suitable LED type for saltwater aquarium?



## thunderdood (Jun 29, 2011)

I'm Eric from Los Angeles. I'm pretty new to the LED revolution going on here. I would like to learn more about LEDs and maybe one day be able to help out others just like me.


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## StarHalo (Jun 30, 2011)

*Re: Hello*

Welcome to the party 

Start your journey here, and feel free to ask any questions.


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## AUKS (Jun 30, 2011)

*Re: Hello*

HI Eric:

i am lisa , nice to know you ! what kinds of led lighting do you perfer to know ?

LED Flashing light , or some nomal light for home and commerical application , as led tube and led bulb .

maybe i can tell you some general knowledge if you like .


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## thunderdood (Jul 1, 2011)

*Re: Hello*



AUKS said:


> HI Eric:
> 
> i am lisa , nice to know you ! what kinds of led lighting do you perfer to know ?
> 
> ...


 

Hi Lisa! I would like to learn more about the Cree LEDs. My biggest hobby is saltwater aquariums. The last few years LEDs evolved and now just might be the next greatest thing not only to light aquariums, but grow plants and corals. I am working on a project to build a light fixture using LEDs to hopefully grow corals in my tank. Right now I am using Cree XR-E Q5 LEDs (Cool white, blue, royal blue). I made a thread about the color temperature in the LED section. And right now I'm wondering why on the specs it says the cool white's are ~6700K, but also have a color temperature range of 5000-10000K. So far I have heard that to change it, I would need to add a blue filter or something onto the light.


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## StarHalo (Jul 1, 2011)

*Re: Hello*

10,000K is going to be very close to cyan, you could just use a cyan LED, or cyans mixed in with cool whites, for light that blue.


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## DM51 (Jul 2, 2011)

*Re: Hello*

Welcome to CPF, thunderdood 

We have a sub-forum for discussing all the various different LED emitter types, so I'll move your thread there.


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## blasterman (Jul 2, 2011)

Thunderdood,

A site like Nano-Reef and their sub lighting forum has a lot more expertise in regards to lighting reef tanks. Hundreds of LED lights have been built over there, many of which on some pretty high end tanks. There's just too much data to go over.

For starters, royal blue and standard blue LEDs (very cyan) are not interchangeable and look totally different. That ratios with white LEDs are different as well with most of no longer using cool white LEDs, and color temp doesn't really have any meaning.


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## thunderdood (Jul 3, 2011)

I have registered there a while ago. I will look at more threads as I haven't really been active on there. I'm more active on another reef forum. Theres just too many to keep up with.


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## thunderdood (Jul 3, 2011)

I'm confused now. Doesn't the color temperature have an important meaning because the plants/corals use a certain color spectrum for photosynthesis? Or are you saying that the individual LED color temperature doesn't matter when set up with whites and blues because the light will be mixed, shifting the color spectrum?


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## thunderdood (Jul 3, 2011)

One more thing, what is Cyan? I have read it a couple times and I have no idea what it means. Is it some kind of color of an LED?


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## doctaq (Jul 3, 2011)

color temp is an average or overall type of measurement sorta, plants and coral use certian wavelengths more effectiveley and higher and lower color temps will tend to have more light in certian wavelengths but white leds usually have a spike in the 450nm range which is pretty good for growth.
the color temp does get shifted when you mix different colors , when you have a lot of royal blue leds and fewer white leds the light might be a 20k or higher, with led color temp doesnt matter as much as with halide or t5 because whites and royal blues put out similar par


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## doctaq (Jul 3, 2011)

cyan is kinda between blue and green..most people dont use them over tanks


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## blasterman (Jul 3, 2011)

Think 'Windex' when it comes to cyan. That's what your tank will look like if you use them rather than royals.

Corals don't care though.


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## thunderdood (Jul 3, 2011)

Thanks for the information guys. I really appreciate it. Is there any equipment in the market that will actually measure the color temperature or the wavelengths?


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## blasterman (Jul 3, 2011)

Again, measuring color color temp is worthless unless you're a videographer. 

Spectral tools are available, but very expensive. Your best bet is doing what everybody else does and put royals on a dimmer and your whites on a seperate dimmer. Adjust to taste.


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## thunderdood (Jul 6, 2011)

Here is what my fixture looks like. All wired up. LEDs are driven at 800mA at 12V.


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## evilc66 (Jul 6, 2011)

How are you setting the LEDs at 800mA? I see no evidence of any LED drivers. How are your LED temps? Seems like a lot of wattage, and not much in the way of heatsinking. Sure, airflow can help situations, but the fan you have on the fixture looks a little small. I'm not trying to bash what you have done, just trying to get you to look a little deeper into your setup to make sure it's running correctly.


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## thunderdood (Jul 6, 2011)

Today I tested the LEDs again and ran them for about 3 hours and they were a little warm but nothing crazy hot so I don't see any reason to put those huge heat sink blocks on them which would make the fixture really heavy. I've also tested them without the heat sinks and they don't get hot either. The LEDs felt the same from 20 minutes to 3 hours. I don't have LED drivers. Just simple ohms law. Here is a schematic of the wiring. Its hard to see but the wires that are thicker have the resistors in them. I also have a potentiometer wired to the lights before the wiring goes into parallel to control the voltage output to allow dimming.


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## evilc66 (Jul 8, 2011)

No wonder your LEDs aren't getting warm. They are currently running at about 100mA with the 15ohm resistor you have them running on, if your diagram is accurate to what you have built.

At 800mA, each of those XR-Es should be running at about 3.5v. With three in series, that leaves 1.5v to burn off with the current limiting resistor. R=V/I, so 1.5v / 0.8A = 1.875ohms. At that current, you will need a fairly hefty resistor to handle the wattage. W=V*I, so 1.5v * 0.8A = 1.2W. Always err on the side of caution, and go bigger on the wattage.

Now, if those LEDs were truely running at 800mA, then you wouldn't be able to hold them in your hand. At 3W, with little to no heatsinking (I don't consider the star a heatsink af any merit), it could get hot enough to burn. It certainly won't live long unmounted.

I'm a little concerned about the potentiometer that you say you have between the power supply and the parallel branches. Most pots aren't really high wattage, and will burn out fairly quickly if you decide to dim the array too low. Like you said, it's simple ohms law. As the voltage drop that the pot has to deal with, the current, and resulting heat (wattage) increases. Dropping voltage at such high current levels is not easy with simple passive devices. There are ways to do it with variable voltge regulators (you would need multiple in parallel to handle the full load), but a dimmable LED driver does this, and many more things.

FYI, those red and blue IDC wire splices are color coded for different wire gauges. The blue ones (16-14awg) are much too big for some of the tiny wires you have connected to them. While they may work now, they may fail in the future. I'd change them to something more appropriate if you have some spare time.

Again, I'm not trying to bash what you have done, or what you are attempting. I've built a few of these () and just want to see you have a reliable system that will do the job.


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## andersonEE (Jul 8, 2011)

Like Evil said...you should replace those 15ohm resistors with 2ohm resistors. With good airflow (saw the fan) your heatsinking looks ok...it depends on how well those aluminum bars are connected to the outer housing. Monitor temps for awhile to verify.


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## thunderdood (Jul 9, 2011)

Great catch guys it makes a lot of sense now. The idea I had was totally wrong. This explains why the LEDs haven't gotten hot. Now I know that the LEDs have a 3.5 voltage drop, but how do know that they each have 3.5V on them? I simulated the circuit in multisim and it also has 3.5V on each LED.


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## evilc66 (Jul 11, 2011)

LEDs are hard to simulate, as they have dynamic resistance in real life. Multisim won't show that, as the change in resistance is related to the die temperature of the LED. The best thing you can do it to set the current on the real LEDs as best you can with a known resistance and source voltage, measure the actual voltage drop across each LED, and then use the measurements to see how you need to adjust things.

LEDs are current driven devices (unlike things like fans which are voltage driven), so at a certain drive current, they have a certain voltage drop. This can be found in the datasheet for the LEDs. It's not absolute though, as there will be some variation, but it's close enough for most estimates, and won't deviate more than a tenth of a volt or so (at least for higher quality LEDs, some Chinese ones can be all over the place).


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## evilc66 (Jul 18, 2011)

Buying a diving flashlight is a bit impractical. There is a ton of information about setting up LED arrays over saltwater tanks out there on the net, just not on this forum. With a little research, anyone can build a suitable setup, without having to resort to buying things like diving flashlights to try it out.


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