I’ve been thinking about stripping the anodizing off a light, as seen in another topic, because it has worn off quite a lot already and looks very used, but then I remembered there was a reason for anodizing heat sinks.
Is there some experience with the effect of anodizing or removing it on a flashlight’s thermal performance?
Not that I recall seeing here or elsewhere, but you might look at djozz’s very interesting thermal test awhile back on anodizing vs powdercoat. You can see that it’s a not-zero difference but also fairly negligible…and by extrapolation I would think that ano vs bare would be much much more negligible. Seems like there may have been some similar comparisons with cerakote but maybe not on flashlights…similar results, though.
Basically mass and surface area matter more than any coating or lack of.
Here is an old cpf post from 2006, where two samples were tested for heat, one was bare aluminum, the other aluminum painted black. The black one was cooler by 65º F.
Unfortunately the pics in the thread are not viewable anymore but the data remains.
Anodizing dramatically increases the emissivity of the surface. This is a measure of how effectively the surface radiates heat to the surrounding environment, and it is the only thermal property that matters for sustained output at a steady-state condition.
At steady-state, the amount of power the LED generates in heat is equal to the amount of power dissipated by the surface of the flashlight body. With the light sitting in air, the latter value is a combination of heat transfer by natural convection and infrared radiation. The rate of heat transfer by natural convection is not affected by any property of the flashlight body material, only properties of the fluid it’s submerged in (usually air). The rate of heat transfer by radiation, however, is significantly affected by the emissivity of the material. In general, bare metals are pretty terrible in this regard while anodized aluminum is pretty excellent. That’s why heatsinks are sometimes anodized.
You can get a sense for the effects using an app called Thermal Wizard, created by Maya HTT. There is a calculator called “Natural Convection around a Horizontal Cylinder” that’s a pretty good approximation of a flashlight sitting in still air. Enter some reasonable values for the size and surface temperature of the cylinder, and you can quickly get a feel for how much more power an anodized aluminum light can sustain at a given surface temperature compared to bare aluminum.