250mm fans on LED heat sink?

Doable sure. Bigger is generally better as you can get more air movement for less rpms and less noise. I would probably just run 2X120s personally (I'm in the process of getting an LED system set up too). That would be enough for 60 3W Crees on that heat sink. How many LEDs are you planning on running on that heat sink? P.s. Andy, this is Matt from Spring 2010 genetics.

 

I have been debating that exact same question about the T5s. I can't see the harm in doing that to tweak the colors exactly to where you want. Are you going 2 RB:1NW or 1RB:1CW?

 

I run 48 LEDs on two 4.25x16 heatsinks. One 3x3 inch fan wasn't near enough per heatsink. They are 24v fans, powered by (only thing I have) a 30v supply. I hooked up a second fan to each heatsink, and it has been way more than I need. I'm working on finding a 24v supply, with the hopes of quieting things down, I know I do not need the fans to be overdriven, they do a great job, and aren't even centered over the heatsinks.

 

I'm running 36 LED's on a 8.5" x 18" heat sink (2" spacing) with a single 120MM fan ($1 each off of ebay). My heat sink stays very cool, even with my XM-L's running at 1.5 amp.

 

$1 fans? Got a link?

 

Here you go:
http://cgi.ebay.com/120mm-Fans-4LED-Blue-Computer-Case-Cooling-PC-/250353053927?pt=LH_DefaultDomain_0&hash=item3a4a3470e7
There's a ton of them on Ebay for that price.   They aren't the nicest fans in the world, but at that price you can buy some spares...

 

Hey Andy, check this out for numerous examples of color blending. http://www.nano-reef.com/forums/index.php?showtopic=246394 The consensus over on nano-reef is 1NW-2RB now on the basis of the neutral whites providing better pop of reds, yellows, and oranges over cool whites. You use two royal blues to even out the color. Actually Royal Blues produce equal or more PAR to white LEDs because they fall right on the 455 nm photosynthetic peak (with Cree royal blues, cheap chinese LEDs are a lot more variable and probably will not hit this peak). I asked on that same forum about adding T5s to the mix. Evil (THE led guy) told me that I would be blown away just by neutral whites and royal blues, but if I wanted a more complete light spectrum, adding a pair of t5s would do the trick. Go with more true actinic bulbs or purple bulbs over say ATI blue + style bulbs as they overlap with the royals.

 

Oh, if you need a par meter to check readings, let me know.  This is over a 120 right?  You're going to probably want 40 degree optics.  Are you going with Crees (XP-G/XP-E?)?  What are you drivers?

 

Andy,

The ELN-60-48 drivers come in 2 varieties. The "D" model use a 0-10V input for dimming. This works with either an Apex (no module needed) or a 10V power source and a potentiometer. The "P" model uses pulse width modulation for dimming. There are a few controllers out there that support PWM and I think the RKE may be one of them.

 

No, you don't need the VDM module. The normal APEX (not the APEX Lite) will dim 4 separate channels. I believe you can do 4 or 5 drivers per channel.

And yes, you can run low power LED's with the APEX (or get the Lunar module from Neptune). You have to use separate LED's though... The lowest setting of the Meanwell drivers is about 10% which is way too bright for moonlights...

 

They are different generations of LEDs for one.  The XR-Es have a slightly higher forward voltage than the XP-Es.  The XP-Es are a bit newer and are slightly more efficient than the XR-Es.  I would definitely get the XP-Es.  Make sure you have the right optics as they have unique optic choices.  Check out http://www.ledgroupbuy.com/ this for cheaper XP-Es.  You are going to get a much bigger difference between XP-Gs and XR-Es, but they only have XP-Gs in white colors.  If I were you, I'd go 2 XP-E Royal Blues to 1 XP-G neutral whites to get the colors you want.  The optics are the same between XP-Gs and XP-Es by the way.  In general, there really isn't a reason to go with XR-Es anymore unless you can get them dirt cheap.

 

Honestly, I think it is probably due to bulk ordering as XP-Es are more popular now.   I hadn't heard anything about them having better radiant flux.  I do know that using the same driver you can drive more XP-Es which, when combined with an increase in efficiency, means a lot more light per watt.   XR-Es are getting old, I wouldn't be surprised if they phase them out of production soon.
I do want to point out that the XM-Ls did come out for white LEDs which are both more efficient and can be driven at a much higher current as well.  If you really want the strongest light possible, XM-Ls being driven at 2-3 amps with optics is going to be blindingly bright, but you'll need 3 or 4 RBs to balance out a single XM-L at 2 amps.