DIY LEDs - The write-up

[Santoki]

Danielrvb,
I think the concerns you outlined are actually where LEDs excel. At ≈4" below these LEDs, there is barely any perceptible heat radiation. Having not enough light is not an issue, as you have already noticed from other users. IME light coverage is an area which may surprise people. If one is expecting a complete even blanket of light which T5s or metal halides tend to generate, then they may be disappointed, as it will require quite a bit more LEDs and/or no optics to achieve that look. Spotlighting (not color separation) will occur with use of any optics less than 60˚ when mounted less than 3' from the tank bottom. But that is where the draw is to many people.
-R

 

[widmer]

Sorry if I missed it somewhere, but can anyone tell me the general difference in efficiency or luminosity of the XP-G's as compred to the XR-E's? I went through the whole data sheet and all I was really able to take away is that the XP-G's come in a ton of different color bins, but couldn't really find much in the way of efficiency.

 

[der_wille_zur_macht]

The Q5 XR-E is 107 - 114 lumens at 350mA. They spec 3.3V at that current. So, it's 1.155w, which means 93 - 98 lumens/w.

The R5 XP-G pulls 3v at 350mA. That's 1.05w. It's rated at 139 - 148 lumens, or 132 - 141 lumens/w.

I used the R5 because it's the brightest I've heard actually exists. The R4 is also out there, which is 130 - 139 lumens, or 124 - 132 lumens/w.

So, the XP-G is about 30 - 40% more efficient. A pretty good jump. Granted though, that's at 350mA, and I don't know of anyone running at 350mA. At higher currents, the efficiency will go down for both LEDs. Though things like junction temperature have a bigger impact on efficiency than current.

It's interesting to compare the spectral plots Cree publish for both cool white LEDs. The XP-G's blue peak is a little lower than the XR-E. It's a very small difference though and probably negligible compared to the difference between color bins for each LED.

Which brings up an interesting point. We all take it for granted that the usual sources give good color bins for Q5 XR-E. They're almost always right in the middle of the plot. I've heard that some of the XP-Gs available have been a little off to one side or another (I would guess because they're still so new?) so it's worth asking about if you're ordering them.

 

[Danielrvb]

Santoki,
Sorry again maybe my wording. I am not conerned about these things. But everyone is trying to avoid them with their builds. I have not seen any tanks that look like they have the "spotlight" effect to me. So I would be interested in seeing a picture of this. With rocks and all, I would think unless there are huge caps, it would be kind of hard to notice. My point is it appears people are overly concerned with cooling, and with over stocking the LEDS to avoid spotlighting, and to have enough power, whe I have not seen any cases where people have had these issues.

willie beat me to the numbers, and I was off a little anway.

 

[Neogenocide]

Santoki,
Sorry again maybe my wording. I am not conerned about these things. But everyone is trying to avoid them with their builds. I have not seen any tanks that look like they have the "spotlight" effect to me. So I would be interested in seeing a picture of this. With rocks and all, I would think unless there are huge caps, it would be kind of hard to notice. My point is it appears people are overly concerned with cooling, and with over stocking the LEDS to avoid spotlighting, and to have enough power, whe I have not seen any cases where people have had these issues.

willie beat me to the numbers, and I was off a little anway.

By spotlighting, are you referring to seeing bars of light in the water column, or actual bright and dark spots on the sand bed.

Scott

 

[der_wille_zur_macht]

I have not seen any cases where people have had these issues.

Heating issues would be hard to qualify, since there are two concerns:

1) Higher junction temp means less output. 50 deg. C can mean 10 or 15% difference.

2) Higher temps would mean shorter life.

Since so few people are taking PAR measurements (much less at different temps), OR setting these things up for 10 years then measuring output loss, it's hard to actually see either of these effects. My take is that too much heatsinking doesn't really cause any problems (even a MASSIVE heatsinksusa heatsink is small compared to a typical fixture) so it's probably better to overdo it a bit.

In terms of spotlighting or poor color blending, I've forced both on my experimental nano builds out of curiosity, and I agree in general - unless you're using tight optics (less than 60 degrees) it would be hard to get either of these problems until you got an LED density well below what we're typically seeing.

All that said, using more LEDs than you think you need means you can run them at lower drive currents for the same end result (same amount of light in the tank). Running at lower currents means more efficiency AND less heat (which in turn means more efficiency), - so it's a win-win.

 

[der_wille_zur_macht]

g bars of light in the water column

IME you won't get that no matter what unless you have very dirty water. What I need is a way to create dirty water for a small amount of time, because I kind of want this effect at certain times during the day.

actual bright and dark spots on the sand bed.

This is what I've always meant - light and dark spots on the sand AND up on the rockwork. It's more likely to happen higher in the tank, especially with optics. With 20 or 40 degree optics closer than a foot or so to the water's surface, you're pretty much going to have a visible light/dark pattern on the rockwork in the highest few inches of the tank, unless you have very close LED spacing (like less than 15 square inches of tank per LED.)

 

[Neogenocide]

The reason I ask is I've got some pics that represent that from a LED build I did on a low wattage freshwater tank. Bars of light in the water column are noticeable, but I don't so much notice spot lighting on the rocks or sandbed. I could post them if someone wanted to see them. And you are correct, it was caused by using optics close to the waters surface.

Scott

 

[der_wille_zur_macht]

The reason I ask is I've got some pics that represent that from a LED build I did on a low wattage freshwater tank. Bars of light in the water column are noticeable, but I don't so much notice spot lighting on the rocks or sandbed. I could post them if someone wanted to see them.

I'd be interested in seeing them. The only times I've seen bars in the water column was when there was a significant disturbance in the tank (i.e. at feeding time, if a bit of sand got kicked up, someone had their hands in the tank, etc.)

 

[widmer]

The Q5 XR-E is 107 - 114 lumens at 350mA. They spec 3.3V at that current. So, it's 1.155w, which means 93 - 98 lumens/w.

The R5 XP-G pulls 3v at 350mA. That's 1.05w. It's rated at 139 - 148 lumens, or 132 - 141 lumens/w.

I used the R5 because it's the brightest I've heard actually exists. The R4 is also out there, which is 130 - 139 lumens, or 124 - 132 lumens/w.

So, the XP-G is about 30 - 40% more efficient. A pretty good jump. Granted though, that's at 350mA, and I don't know of anyone running at 350mA. At higher currents, the efficiency will go down for both LEDs. Though things like junction temperature have a bigger impact on efficiency than current.

It's interesting to compare the spectral plots Cree publish for both cool white LEDs. The XP-G's blue peak is a little lower than the XR-E. It's a very small difference though and probably negligible compared to the difference between color bins for each LED.

Which brings up an interesting point. We all take it for granted that the usual sources give good color bins for Q5 XR-E. They're almost always right in the middle of the plot. I've heard that some of the XP-Gs available have been a little off to one side or another (I would guess because they're still so new?) so it's worth asking about if you're ordering them.

WOW ~130-140 lumens per watt! If I remember correctly, that's 1.5x as much light per watt as T5HO, and 2x as much light per watt as NO fluoros & metal halide. That's serious efficiency. When also factoring in the cost of replacing fluoro bulbs, it's looking light LEDs may be slated to replace standard office/industrial fluorescent lighting all over the world.

And then I wonder how much more efficient they would need to become before they're producing virtually no heat, so that people wouldn't need big heatsinks and fans, and would maybe just use a little aluminum plate instead for mounting, creating some paper thin fixtures...

 

[Neogenocide]

ok...here they are...built for my 125 African Cichlid Tank.

12 CREE XR-E Q4 Cool White 3W LED

First pic is a few inches off the water with no optics

Second pics is a few inches off the water with 60 degree optics. I had a filter cranking out microbubbles at the time, what a pain.

Third Pic was taken at about 8" off the water with 60 degree optics.

Given, as der_wille_zur_macht said, anything in the water column will make the spotlighting more visible, as shown in my pics. Since solving the bubble problem, it is less noticeable, but you can definitely still see it, represented in the last pic. It was taken after the offending microbubble filter was taken out.

Scott

 

[widmer]

IMO that's kind of a fun effect. Reminds me of when I was younger and would go swimming at my grandpa's cabin. Due to floating seaweed etc, there were very noticeable streaks of light in the water like that...

 

[Santoki]

here's an example of nice spotlighting:
http://www.reefcentral.com/forums/showthread.php?t=1669396
For those who might be too lazy to click...
timmmysli's tank:

 

[der_wille_zur_macht]

IMO that's kind of a fun effect. Reminds me of when I was younger and would go swimming at my grandpa's cabin. Due to floating seaweed etc, there were very noticeable streaks of light in the water like that...

I agree - thought it would have to be applied artfully. I LOVE the "beam from heaven" when clouds part on a stormy day, or when you're down below the face of a reef and light pokes through a hole in the rocks.

 

[james3370]

Maybe I am just blind, but I am not seeing the good price on this top secret site.
Maybe you can talk more code to lead me to it.

took me a minute to find it....last time it was in the lighting forum, but this time in the "for sale" forum

http://www.nano-reef.com/forums/index.php?showtopic=218538

 

[Danielrvb]

aahh... there it is! Thank you. That is good prices, but for how many I want to order right now, that shipping nearly kills it. But thank you very much for the link!

Those pictures are very useful, nice to get a real visiual of the cone made by the LED, and with an optic. And you can see that even with that you dont really see the beams on the sand and rocks.


as far as efficiency goes, yeah its better to run them efficient. But people seem to be over doing whats needed. When your running 10-20% more LEDS at a more efficient rate, is it really more efficient? what is the rate they lose by driving them higher? That I am not sure of. Really we could figure out which way would be better, but would need to see some minimums for what is acceptable first.

 

[crank2211]

Hi guys,

I just stumbled on the beginning of this thread yesterday and made it 1/2 way through the first split before realizing I had another to go.

I'm planning out this build now, and think I've got everything figured out except how to wire up the 24V 6.5A power supplies to the BuckPucks. I was looking to go with the 1000mA dimmable's w/ pots.. 4 rows of 6 on a PS. So my question is, are there any details on how to wire these up? Will all 4 BP's get tied together and meet at 2 terminals (+/-) on the Power supply? Are there any pictures of this setup somewhere?

Thanks!

 

[der_wille_zur_macht]

Crank, it's pretty straightforward. The power supply will have a + and - connection for the output (24V DC) side. Connect ALL + leads from the buckpucks to the + terminal, and ALL - leads to the - terminal. You want them in parallel.

Some power supplies actually have two or more pairs terminals for the output, just break them up evenly between the two.

 

[crank2211]

Great! I was hoping it was just that simple..

Thanks for the quick reply, der_wille

 

[widmer]

Question for anyone who knows electronics:

For those of us who are using buck pucks which are at least 18" from the power supply, and thus should be using a 50V, 220 uF capacitor across the buckpuck's input terminals(see buck puck data sheet on ledsupply website), does this capacitor fit the bill?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P13131-ND

I basically singled in on it because it looks like it has the longest life span. But I don't know if the +/-20% tolerance makes any difference, being that we're pretty much all using 24V power supplies...