As far as cooling during the burn-in, I believe the test setup would be as good as, or better than, a flashlight for the following reasons:
1. The LEDs are exposed to ambient airflow instead of being enclosed in the head of a flashlight.
2. The leads were not trimmed (more direct heat radiation surface)
3. The power source was separate from the LED, so its heat generation did not affect the LED.
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While I agree generally with your assessment of the utility of this experiment, I think that the test set up described is actually inferior to the heat sinking provided by a metal flashlight. A few examples;
1) If you put your hand in the ambient airflow over the burner on your stove, does it burn as quickly as if you put your hand on the burner? Direct contact is always the most efficient form of heat transfer, and the metal head and body of a flashlight have a significant thermal mass. This thermal mass would have to be overcome before the internal LED temperature could rise much.
2)For short bursts, heat would be moved away from the chip very rapidly by the large thermal mass of the light body. I doubt the thermal mass of the lead wires amounts to much. In longer bursts, the metal body, with it's high conductivity, would move the heat into your hand or the air much more rapidly than the low conductivity epoxy and two wires could into the air alone, so in either case the flashlight would be better off.
3) This very well might be true, depending upon how efficient the circuit is and how well it moves it's own heat to the body of the light. This is a definite design variable, but it doesn't overcome the huge difference in thermal mass between the air around this test set up and the metal body of a torch.
It may be futile to post to a dead thread, but I love a good thermodynamics conversation. :rock:[/QUOTE]
Good comments.
I believe they would apply well to a Luxeon type LED application. I have not personally seen any 5mm LEDs in flashlight applications with the effective 5mm LED lead to flashlight body thermal conduction you mention above. Many manufacturers seem to think those 5mm LEDs don't generate enough heat to warrant any thermal releif.
Paul