LED lighting on a budget!

What is a "good" price for a CREE XR-E?

What is a "good" price for a CREE XR-E?

I see a 1 pc price of $4.99 US for a single XR-E emitter from LED-DNA, an e-Bay store. Does anyone have an idea of what is a "reasonable" price range for these?

I would like to apply this thread to my new 180. 24x72x24 deep, trying to determine how many I require for a "softie" and LPS setup.
 
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You'll need about 100 LEDs or, whatever number around that, that matches up to the drivers you can find.

Prices? I'm not up on that.
 
Depends how many your order. Deal extreme maybe cheaper. In quantity you can get XP-E RP for $2.82 and XP-G CW for $4.51. Are you in WAMAS?
 
On the U-channel from home depot, is there some kind of guideline for spacing? If I'm needing to light a 120 (2x2x4) with 96 LEDs, that's 1152 sq in meaning roughly 1 LED for 12 square inches, or 3.5" on center.

If I basically join a bunch together in a lattice type design with flat sections and U-channel on top, is this going to provide enough heat wicking capability, as long as I use a couple fans?
 
That sounds like enough. Just make sure you aren't jamming the neighboring U s up to each other or you won't have any convection surface.
 
Also moun tthe LEDs to the U channel no the flat. Unless you use thermal compound between the two there will not be good heat transfer and it will still be hotter on the ones the LEDs are mounted to.
 
Terahz built looks NEAT, but this thread is about saving as much money as possible, right?

If you mount the LEDs directly on the U-Channels, you'd be saving a lot of money.

Terahz built, for example, would have cost him $41.28 for the heat sinks + $21.02 for U-channels.

Mine, with the same number of LED's, cost me $21.02 for the U-channels, and ~$6 for 2 fans.
 
True, you'd need to add the electricity cost to run those fans, although some people say they wouldn't even be necessary.

Perhaps people using u-channels as heatsinks can chime in on their experience.
 
I think there is a balance to consider. The L70 lifetime of LEDs will shorten in relation to the running temp of the lamp (junction temp, whatever, I know I'm not using the right term, but you know what I mean). Therefore, keeping the temp as low as feasibly possible is really the goal here if you want to maximize long-term efficiency.

I'm an EE in the consulting/design field, and a recent seminar I went to covered this issue quite a bit. There is a boom in the aluminum industry right now due to LEDs becoming the fixture of the future.

I see big honkin aluminum heat sinks from places like heatsinkusa used on DIY LED fixtures and I just have wonder if it big time overkill.

The "U" or "C" channel aluminum to me seems like it's the opposite - underkill, which is why fans are needed.

I think terahz's solution is ideal, because it provides adequate heat removal from the junction without wasting aluminum or money, and required no active cooling. Granted that it is open-air, so put in an enclosure I would assume some air movement would be a good idea, but I think it would be much less and not direct (no fans blowing directly on the heat sink, just air movement in and out of the enclosure). This overall design should keep the junction temp down and extend the L70 life (or not decrease it rather). So from that perspective, it may be the true money saver.

I haven't thoroughly searched this site yet, but I have yet to see any hard data that shows that the junction temp is maintained at an acceptable temperature with Aluminum channel. I have a feeling that it is probably running on the edge of the acceptable limit, and while that may be OK, I'll opt for a little more protection.
 
Unfortunately we can't measure the junction temperature. The best is a IR thermometer pointed at the star. No everyone has these. So the next best is can you leave your hand on the heat sink? If so it has been considered in the safe range.

Do you suggest something else?
 
Floyd R Turbo said:
I haven't thoroughly searched this site yet, but I have yet to see any hard data that shows that the junction temp is maintained at an acceptable temperature with Aluminum channel. I have a feeling that it is probably running on the edge of the acceptable limit, and while that may be OK, I'll opt for a little more protection.
Click to expand...

So this is my question? What is the acceptable temp without fans? Im using 1" square tube. 3" between HP LEDs. 95 degree F running at maximum.

Am I killing my LEDs?
 
You are probably fine. How close to the LED are you measuring? There is a big difference close to a far away. Can you measure the star right were the LED sits? IIRC the best place to measure is the back of the star center. So the best temperature is probably the heat sink directly opposite the center.
 
Temperature..

While some effort is required in this direction almost all the builds we're seeing, with the exception of Stu's:lmao:, are massive overkill. Note my recent build. That's just 0.063" Al with some simple fins. Even that is more than necessary! We should step back and recognize that trying to get 10 years out of these fixtures is folly.

Look how far the state-of-the-art HBLEDs have gone in the last 3 years. We are at 100 lumens per watt now. It is expected that we will be at 150 lumens a watt in something like 2 years. Are you really going to want your same old fixture running over your same old tank in 10 years, when your fixture is costing you perhaps three times more to run than a newer fixture? That's way after the time you should've recycled your present one just to save energy costs.

Spending a fortune on aluminum and running 6 fans for a wind tunnel sound effect is not the way to go.

I recently researched this for my build.

How hot?

This is how hot:

One hundred fifty eight degrees F directly behind the center of the star on your heatsink's base metal - not fins - is where we should be aiming.

That puts the LED's operating temperature on the far far left of the recommended operating curve for lifetime. The curve goes far to the right from there. How far? The curve goes to 302F!!!

So, even though in the past I've suggested if you can touch it you're certainly cool enough I've changed my opinion. With my new understanding I'm upping that recommendation to a value that actually makes more sense. 158F

158F is instantly painful to the touch. That's a reasonable temperature - as far as the HBLEDs are concerned. At that temperature the L70 is still seventy thousand hours that's 19 years!!! LEDs will probably be 1000 lum/W by then and our fixtures will be long dead, economically and aesthetically.

Save some money and start aiming for too hot to touch directly behind the LEDs and really, really warm heatsinks.
 
TheFishMan65 said:
You are probably fine. How close to the LED are you measuring? There is a big difference close to a far away. Can you measure the star right were the LED sits? IIRC the best place to measure is the back of the star center. So the best temperature is probably the heat sink directly opposite the center.
Click to expand...

this is pointing at: the emitter, the star, the solder points, and contact between star and alum sink.

And based on Kcress latest research, my rig right now is fine and safe.
 
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