Jarhead
Banned
Sorry for boring the light cannon vets, but for the new folks, a reminder is useful...
Take a look at the light output verses temperature on the Luxeon datasheet.
The light output is heavily dependent on the die temperature.
The cooler you keep the Luxeon, the brighter it is. You can loose an easy 40% or more of your light just because you don't keep the emitter cool.
Folks who try to keep and LED cool on a FR-4 board with
one layer of copper running to the flashlight body are
just loosing out hardcore. It is due to the thermal
resistance of that super thin layer of copper, doing a
very poor job of tranferring the heat, due to it's thermal
resistance.
PCB Weight Copper
(oz/ft2)...(mils)
1/2........ 0.7
1 ......... 1.4
2 ......... 2.8
3 ......... 4.2
Most consumer PCBs are 1/2 or 1 oz copper, which means the copper thickness is just like foil, 0.7 to 1.4 mils thick, or 0.007" to 0.0014" thick. This makes for a nice thermal resistor. Luckily in most flashlights, the distance isn't so short that we don't incur major thermal resistance in the super thin copper layer and cause big issues.
If you want to get more light, mounting the emitter to a slug that is 0.090" of aluminum, or 0.030" of copper, will do a very nice job of tranferring the heat from the Luxeon to the flashlight housing. Thermal epoxy is highly suggested for mounting the emitter to the metal slug, and either thermal grease or thermal epoxy between the slug and the flashlight housing will also help.
Take a look at the light output verses temperature on the Luxeon datasheet.
The light output is heavily dependent on the die temperature.
The cooler you keep the Luxeon, the brighter it is. You can loose an easy 40% or more of your light just because you don't keep the emitter cool.
Folks who try to keep and LED cool on a FR-4 board with
one layer of copper running to the flashlight body are
just loosing out hardcore. It is due to the thermal
resistance of that super thin layer of copper, doing a
very poor job of tranferring the heat, due to it's thermal
resistance.
PCB Weight Copper
(oz/ft2)...(mils)
1/2........ 0.7
1 ......... 1.4
2 ......... 2.8
3 ......... 4.2
Most consumer PCBs are 1/2 or 1 oz copper, which means the copper thickness is just like foil, 0.7 to 1.4 mils thick, or 0.007" to 0.0014" thick. This makes for a nice thermal resistor. Luckily in most flashlights, the distance isn't so short that we don't incur major thermal resistance in the super thin copper layer and cause big issues.
If you want to get more light, mounting the emitter to a slug that is 0.090" of aluminum, or 0.030" of copper, will do a very nice job of tranferring the heat from the Luxeon to the flashlight housing. Thermal epoxy is highly suggested for mounting the emitter to the metal slug, and either thermal grease or thermal epoxy between the slug and the flashlight housing will also help.
