On Sun, 7 Oct 2018 20:37:59 -0700, sms
wrote:

On 10/1/2018 6:29 PM, Jeff Liebermann wrote:

snip

Let's see what the package can do as a heat sink.
Latent heat for aluminum is 0.900 Joules/gm-K.
The light weighs 142 grams, which I'll assume is mostly aluminum.
The light dissipates 71 watts with all the LED's turned on.
I would guess that 75C would be uncomfortably warm for both the
electronics and the bicycle rider. That's a temp rise of 50C (50K).
Joules = Watts * seconds = 71 watts * seconds. Therefo
0.900 = 71 * seconds / (142 * 50)
Time(sec) = 900 seconds = 15 min
Not too horrible. One has 15 minutes of full brightness lighting, in
still air, before the LED's burn your hand or cause a thermal
shutdown.

They even admit that full power requires sufficient airflow requiring
moderate speed to prevent throttling.

Yes, and they little to improve radiation cooling by increasing the
surface area.

A long time ago, one poster here was insisting that one reason LED
lights were so wonderful was the lack of a "white-hot filament." What he
failed to understand was that a high wattage LED has a very hot
semiconductor junction and that extracting the heat from that junction
is a very difficult process, more difficult than cooling an incandescent
or HID lamp. Some LED lights for cars even have fans as part of the
thermal solution.

It doesn't matter how the heat is generated. It could be a carbide
lantern producing the heat, and it still needs to be radiated or
conducted away somewhere.

Still waiting for liquid cooled bicycle lights. I was over at the
Computer History Museum last week where they have several liquid coold
computers on display.

"liquid cooled 500W LED bike lamp"
https://www.youtube.com/watch?v=hYxrpHTEEEQ (6:23)
40,000 lumens. I suppose that dumping hot water on the trail would
work for a while. Otherwise, collect the hot water and use it to make
coffee during the ride.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558