L.E.D. vs HALIDE/T5/VHO

[OceanicCorals-Eugene-]

Originally Posted by sphelps

Ok well these ones you sell come to mind

Like Ron has already pointed out, these lights alone, weight about 1- 1.5bs Also these lights run at a temperature of roughly 50C, the whole debate about whether or not we need fans for the fixtures was the debate on how efficiently the heatsinks alone can dissipate the heat to keep the temperature as low as possible. At 50C the LEDs will surely work close to there rated 50,000hrs life time. But the decrease in intensity will be larger over the course of the bulbs overall life.

Originally Posted by sphelps

Also you could use a peltier system and regulate the current with a simple thermo switch so the surface stays at a consistent temperature just like fans so condensation would be no different. As long as the surface temperature stays at or above ambient you won't get condensation.

The bottom line is many high powered systems already exist which don't use fans so it can be done and it can still be done better. I'm not sure why you all feel the need to debate that, if you like fans go nuts but I'd prefer a system without fans. It's a simple personal preference I guess, and I'm entitled to it.

A peltier system wont work without a fan im afraid, you need something to cool the hot side of the peltier or it ends up heating up both sides, so either way there needs to be active cooling in the use of peltiers.

again the debate on whether or not fans were needed started based on the idea of keeping the heatsinks as cool as possible. But a system without fans will work, just not as efficient as those that has active cooling, as you'll most likely see an increase in intensity drop through the life of the emitters.

Originally Posted by sphelps

I have some of the LED spotlights in use in my house, they are actually about the same weight as the halogens, much lighter than they look. A little bigger but certainly not heavier. The larger size is also due to need to include a driver not so much a result of the heat sink. The size difference is also only noticeable on the very small spotlights, pretty much every other type of house hold bulbs are of each size.

Keep thinking that if you want but you don't have to add more weight to increase heat sink efficiency. Applying individual finned heat sinks to each LED will not add significant weight and reduce the the need for an additional large heat sink. You could very easily decrease the weight of the fixture with proper design. LEDs don't generate a lot of heat, they are at least 90% efficient meaning a 3W bulb can't produce more than 0.3W of heat which is very little. The reason you need fans is because you're simply bolting one side of the of it to a large aluminum plate which isn't a very efficient way to remove the heat.

Applying individual finned heatsinks to each LED would create uneven cooling to each of the heatsinks. unless your talking about a fanless system, if thats the case then you'll need some fairly well designed light weight heatsinks. If we were to mill the front face of the aluminum heatsink with fins down to about 1cm would it increase the efficiency? It'll move the heat towards the fins faster, but without active cooling/air movement your not doing much with the extra speed in heat transfer from the LED to the heatsink.

Maybe we'll see a fixture out there in the future that will be fanless and be able to keep the temperature at 30-40C, when that day comes i'll purchase one to test and throw a fan on top to increase the lifespan of my LEDs(highly doubt it but i want to be optimistic)

[StirCrazy]

Originally Posted by OceanicCorals-Eugene-

At 50C the LEDs will surely work close to there rated 50,000hrs life time. But the decrease in intensity will be larger over the course of the bulbs overall life.

actualy a temp of 50 degrees is well with in the specs that the LEDs are rated at so they should do better than the rated hours and less intensity drop that the spec since the specs are at 80 degrees.

I will agree that there is the ability to create a heat sink that could keep temps down to 40 degrees but it would be in a controled enviorment.

the problem I have with Passive cooling is that there is so much requirement for "space" around the fixture so the heat has some place to disapate to. so you would have restrictions ie. no use in a closed canopy, must be so far away from surfaces to ensure good air movement around it. must be used under a specific ambiant temp, and possibly must be used in low humidity unless some other means of suplementry air flow is provided.

Just like the spot bulbs that are being sold now, if the air access to them is restricted in any way they burn out as they found when people were using them in closed fixtures.

the problem with high humidity is it can actualy form an insulation barrier around the heat sink preventing cooler air from getting in contact to adsorb the heat efficently.

so many factors involved, and you guys are making me have to remember all my coursing in theromal dynamics which hurts my head lets just agree while it would be nice to have a pasive system, a active system of some sort that will not condense moisture in the air will be the best answer, but I will add a few things and give away a couple things that I am building into my system as I am going opposite of Ron as I am starting with the controler, but I have the time to do it that ways.

you don't need much air flow, and if done right you will never hear the fans. by using the fans you can get away with larger spacing of the fins on the heat sink and also use shorter fins, reducing the hight and weight of the fixture. now I will be playing around to insure that even with out the fans I stay under 75 degrees in an operating enviorment, and I will be incorperating a shut down feature into the micro controler which will shut off every second LED to reduce the amount of heat going into the sink and enable it to cool its self off. if the heat still goes up it will shut off all lighting. I am aiming to have the fist stage kick in at 45 degrees and the second at 50. I am also toying with the idea of fan redundency so therte is another set of fans on the heat sink that only come on if the system hits a specific temp. now the temps I have listed are just off the top of my head, maybe the secondary fans will come on at 45 and everything else will be bassed off that, still have to play and figure out what I think will work the best.

Steve

[OceanicCorals-Eugene-]

Originally Posted by StirCrazy

actualy a temp of 50 degrees is well with in the specs that the LEDs are rated at so they should do better than the rated hours and less intensity drop that the spec since the specs are at 80 degrees.

A running temp of 50C it is still within the range of acceptable temperature for the LEDs. They are spec to run at 50-80C max but with cooling you can actually prolong the life of the LEDs and get less intensity drop over the claimed 50,000hrs life of the emitters.

I agree with you that it would be nice to have a silent system, but in the long run i just dont know if its worth it, i mean we can get more life/intensity out of the LEDs if they were active cooled than passively cooled so why not do so and gain an extra few years more out of them.

You've got some good points there Steve, it'll be interesting to see your project on the LEDs too

[bakaichi]

i thought i might put this on

Normal running temp for the CooLED at room temp of 23 C is about 50~55C

just by simply adding a computer fan to help heat dissipate, the temp is down to around 37~39



Pic here you can see the fan and the light operation.

The heat sink, pluse a little bit of active cooling decrease the running temp but a lot .


~~

[OceanicCorals-Ian-]

Here is a recent quick review of the LED Aqua Illumination module. Note the PAR comparison.



http://reeftools.com/news/aqua-illum...ar-led-system/

[StirCrazy]

Originally Posted by OceanicCorals-Ian-

Here is a recent quick review of the LED Aqua Illumination module. Note the PAR comparison.



http://reeftools.com/news/aqua-illum...ar-led-system/

yup, nice output but there 24" is from the top of the aquarium, they forgot to include the 2" the modual is above the tank so there 12 and 24" measurments should actualy be labled as 14 and 26.

Steve

[Lampshade]

For Cooling check out this online calculator:
http://www.novelconceptsinc.com/calc...resistance.cgi


Cree has a page regarding thermal management:
http://www.cree.com/products/pdf/XLa...Management.pdf
And their page about XP-E's:
http://www.cree.com/products/pdf/XLampXP-E.pdf

Sooooo.... I'm planning on a build with 120 LED's. The Thermal Resistance in the LED's are 9°C/W(XP-E Blue/White) and a good junction to the heatsink is 1°C/W per LED i can calcualte the minimum heatsink resistance needed driving them at 750mA at an ambiant 30°C(my house has AC, should never get that high). Thermal resistance is how much hotter something gets to disapate 1W of heat, so lower is better for a heatsink.

Aluminum is about 237 W/m*K at 26 Celcius.(wikipedia)

Use the formula for Heat from cree:
Tj = Ta + Ptotal (Rth j-sp/ NumLED + Rth sp-h + Rth h-a)
P = 120*.750A*3.25V = 292.5W
Rth h-a = (145°C - 30°C –9°C/W x 292.5W/120 – 1°C/W x 292.5W/120)/292.5W = 0.31°C/WIn

I need a min 0.31°C/W heat sink.

Using the calculator on novel i can find the size i need to meet that. I used the slab calculator and the one linked above and came up that a 10"x42" heatsink with 1" fins and .25cms of air flow, asuming .25cms average flow over the entire thing, 1 computer fan is .25, it would probably take 2 to make this consistant. This would have a C/W of : 0.0653926108°C/W, far more than needed.

Couple other pages for info on Cooling LED's:
http://www.qats.com/cpanel/UploadedP...a_0909_web.pdf
http://sound.westhost.com/heatsinks.htm