On Sun, 05 Mar 2006 05:16:51 GMT, Ernest Christley
wrote:

Andrew Sarangan wrote:
Hello

It was my impression that mounting the LED directly to the reflector
(flashing aluminum) will not provide enough heat sinking. A large
surface area is not the only determining factor because the thermal
conductivity of the metal will limit how far the heat can spread. The
thinner the metal, the worse the thermal conductivity. Flashing
aluminum is only 1/100" thick so its conductivity is not very high. One
could construct fins on the back side to increase the surface area, but
commercial heat sinks do that much better.


I think you have a beautiful design with good tradeoffs, Andrew.
However, if one were inclined to go fanless, there are heatsinks now
that are much lighter will provide much greater surface area. It uses a
much greater number of fins, and each is very thin.

Ernest, it takes cross sectional area to conduct heat; if you look at
the TRULY designed heatsinks to maximize heat transfer to air, you
will note a tapered base with tapered fins, larger and thicker fins
close, smaller and thinner further away.

I am weak in describing this, but I think you will get the picture;
think about holding a piece of aluminum foil 2 inches long in a candle
flame, then a piece of 1/4" aluminum rod in the same flame. Your
fingers won't get warm with the foil, but will burn with the rod.