thermal conductivity

[GTSECC]

Of Aluminum is much better than brass.
Why would anyone make a brass heatsink in an aluminum light?

 

[xenonk]

Brass is significantly cheaper and is easier to solder to for, say, an electrical ground path.

It also has higher mass/specific heat capacity. It takes more thermal energy to raise the temperature of a given volume of brass by one degree. The higher heat conductivity of aluminum or copper is better in the long run regardless, though.

 

[Marduke]

Because thermal conductivity is only part of the equation. Thermal capacitance is another. When you dial the knobs of heat source, heatsink mass, surface area, material (thermal conductivity vs capacitance), weight, cost, ease of machining, etc., sometimes (often) brass comes out as a superior heatsink material.