EEVblog #50 - Solid State Cree LED Lighting, and How Thermal Design Sucks.

Dave lights up his new backyard deck with Cree XPG LEDs, and then winds up measuring the wind from a storm instead. And do you know the difference between efficiency and efficacy?

[rkan]

Lol... Did diodegonewild make his spotlight CFL video by chance? The lights he took apart look very similar to the ones Dave showed at 0:35 :D

[swolebro]

Dave! I'll binge watch from the start. Maybe I'll catch up by 2030! Thank you for all the work you've done over the years! You've filled in many of the (many many) knowledge gaps in this physicist/software developer's education.

[OrenMitz]

One of the better videos I've seen of your's - Dave. Funny and highly efficient...

[Irilia_neko]

Interesting project, and interesting to have the results 11 year after ^^

[EEVblog]

@jasonuscg It's called a conversational off-the-cuff style. If you think it's too long then you go redo it in 7 minutes. I'll give you a week, but remember - no script and no retakes - I'll trust you. Once you are done, post it as a video reply so we can all critique your style.

[nwimpney]

Another issue with efficacy to efficiency calculations is that chromaticity of your light can make a really huge difference.

Most likely the efficiency of your leds is actually a lot lower than you calculated, because they tend to be fairly high in the green/yellow region in order to get those amazingly good numbers. Also, they're probably measuring the efficacy at 350mA, and not 700.

Regardless, they're pretty amazing, and unlike a lot of the other power leds they look reasonably natural.

[EEVblog]

@OldSkull87 Impossible to say unless you have the reliability specs for the LED in question and you can accurately measure the junction temperature. The generic answer is "as low as possible"

[jonharkulsykkel]

seeing that drop in the temperature graph got me thinking about the possibility of making a "windometer" or whatever based on this effect. of course after some googling it was already invented, check wikipedia "hot-wire anemometer", its pretty much the same thing and apparently those devices are used for studying turbulent flow. interesting

[wjrable]

I don't know if someone has already noted this but the maximum possible efficacy of a light source is 683 lm/ W, for the case of monochromatic 555-nm green light. The maximum possible efficacy for an ideal white light source is 240 lm/W because the human eye is less sensitive to wave- lengths on each side of green.

[pikuorguk]

I've got a Tesco brand 3W Cree LED torch which runs from two C cell batteries. It seems to use the torch body as a heatsink, and after a few hours running it gets "a bit warm". I'm guessing its batteries will run out before the torch heats up enough to damage the LED.

[EEVblog]

Did you check the heatsink compound undernearth? If that's not in good nick then you might indeed have a problem.

[FenderGibsonWashburn]

I think LEDs are fascinating. I believe LED lighting will become more popular as people start to look into other alternatives to incandescent lighting besides CFLs. Lumens per watt are going up and prices are coming down, very exciting.

As far as Thermal Design goes, overkill has always worked for me.

[danptl]

oh how i love Dave!! Thank you brother, i learn so much watching your videos.

[philbx]

Hey Dave, nice work again.
I've been stuffing around with LEDs for many years and haven't gone into thermal calculations, instead just used PC heatsinks.
It's amazing at what extents people go to in trying to get an 'optimal' cooling setup (candlepowerforums).
Got a torch from dealextreme which doesn't seem to have much control circuitry. (SSC-P7) but the damn thing works great, maybe due to good Chinese engineering and much aluminium OR more likely just the "guess it'll work OK" factor.

[shodanxx]

thermal conductivity of aluminium is 237 W·m-1·K-1 according to wikipedia
it's high, that's why you didn't get "hot spot" or large differences between your half quarter and under button
if you'd used "angle iron" aluminium you would have gotten better convection cooling and even better with a couple vertical fins
a thicker aluminium strip would ramp up slower but the plateau would be the same temp because the choke point is how much convection you're getting so only higher surface would cool it

[debug_duck]

I plan on using LEDs to light my room and of course I want to bulild my own :). As 5 years have passed now, I wonder what the best LEDs now are. They need to be warm white. I already tried some cheap 10W LEDs from ebay but they weren't that great.

[kolrabi]

In the U.S. some engineers didn't bother to do thermal calculations either and put LEDs into traffic lights. Now they don't generate enough heat anymore to melt any snow blocking them.

Google for 'led traffic light snow' for more information. ;)

[vijayakrishnankuttinath]

Dave, @19:09 is it the high junction temperature causing the sensation on the finger? Or it's the ir spectrum of the light emission

[inactivated]

Dave the way you were holding the whiteboard and pen reminds me of a violin player.

[BocaNejra]

Your video was very interesting although at the end It didn't clear a lot of things up in terms of calculating the needs of dissipation or heatsink measures. I'm designing a led light panel for aquarium light with 4 modules of 7 led stars (14W each) and I'm trying to figure out the heatsink I need for passive refrigeration (no case or fans, all open for maximum air circulation) and it's getting quite tricky! :(