Thermal conductivity of aluminium oxide: 30Wm/K
Thermal conductivity of hard anodized aluminium: 4Wm/K
The heat emissivity of anodized aluminium is still many times higher then polished aluminium though.
Thinking out loud. 
Your point being..? :P
Interestingā¦
Motorcycle engines, particularly heads, are left rough cast or sandblasted, because they exchange heat faster and better than polished ones.
Also, think about how car radiators work. Very thin copper or aluMINIum (:P) with a huge surface area. No real thermal mass, although an engine has quite a bit for strength and stability, both thermal and structural.
it is a good thing that we do not build flashlights of aluminium oxide, but only add a very thin layer.
The thermal mass is in all the fluid in the radiator along with the engine block the heat is taken from.
some motorcycle engines are coated with a thermal conductuctivity coating(yamaha). and Thermal Barrier Isolation and Conductivity ā Swain Tech Coatings | Industrial Coatings | High Performance Racing Coatings can coat your parts to improve the thermal properties.
If one can calculate the thermal shedding (technical term i know) of anodized aluminum by temperature and surface area, and demonstrate that different types of anodization are similar, it would be very helpful in flashlight modding and selection
I have an A60 host on hand which has a layer of anodizing between the LED star and the aluminium, I am thinking I will be grinding it back to the aluminium before inserting a Sinkpad into the mix. As for why this thread exists: not all know the above informationā¦ I only just discovered it myself.
Anodizing helps with thermal radiation (emission of heat as infrared light) from the surface of the aluminum. Radiation does not require airflow, which is good. Also, anodizing does not have a significant impact on thermal conduction, so heat is still conducted to the ambient air.
Since radiation is basically light, I consider it this way. If the material is shiny/reflective, it does not absorb light well so it cannot radiate light well. It may sound strange but just light light is reflected away, the shiny surface also reflects infrared back inside that wants out.
Your standard issue tinfoil is a good example; only one side is shiny for a reason.
A shiny anodize does not hep with radiated heat like a good matte finished anodize.
I have two identical lights with the two types of anodized finish. I find that the black anodized light does not get as warm as the shinier grey anodized flashlight. This has not been heavily tested as I did not do simultaneous tests with the same exact power input, however the difference in operating temperature is much greater than the difference in input power.
HA-II and especially HA-III anodized aluminum have much higher thermal emissivity than a shiny anodized or un-anodized aluminum. Itās about an order of magnitude better, in fact.
I do not think the difference will be measurable, however I would not āgrindā it off. You want the interface surface as smooth as possible. Use a very fine emery paper (maybe 800-1000 grit minimum, I use 2000 to improve thermal contact surfaces) to remove only the anodize and leave a shiny surface behind. This maximizes the contact area between the surfaces which is what you want for conduction.
Wow, thatās cool. So I can put any material with a high value of thermal resistivity (low value of thermal conduction) in my heat path, and it wonāt hurt the conduction! How exciting! To hell with copper, Iām using bubblegum from now on.
PPtk
WTFROFLMAO, I about crapped myself. :bigsmile:
You almost exploded my sarcasm detector 
Anyway, yes, the anodize layer is not the best thermal conductor, however itās thickness is usually measured in microns.
If your concern is that this thin layer will significantly reduce heat conduction, then you should be fine with a 0.003ā layer of household insulation for your home.
Seriously though, if your product relies 100% on conduction and doesnāt need environmental protection (ex. CPU fan) definitely do not anodize it.
In the case of a flashlight, Iāll take the (minor) thermal conduction hit of a nice HA-III anodize, knowing it has superior protection and thermal radiation properties.
Anodic coatings are not super thick, Iāll give you that. Saying that āanodizing does not have an impact on thermal conductionā, however, is flat wrong. Per MIL-A-8625, Type III Anodic coatings are typical 2 Milās thick. Thatās more than a few microns. To be within specification, Type III can be as thick as 4.5 Milās (.0045 Inch). Does it make a huge difference in conduction? Probably not. Does it make a difference in conduction? Yes.
PPtk
Ok fixed, for accuracy.
Edit: I guess 100 microns is more than a few, but still verrrry thin. The OP conductivity number is not sourced, but it is close to an order of magnitude too. If it really is that significant of an insulator at 100 um, then I want 6ā thick batts of it for my house.
Think of it like the dielectric layer in traditional MCPCB vs a Sinkpad boardā¦ granted the effect will be smaller then that caused by the dielectric in MCPCBs but it is still there. I believe its the thermal bottlenecks between the torch body and the LED that have the most effectā¦ once the heat has been passed to the body it is free to spread out and emit off.
In an ideal / perfect situation the junction temperature of the LED will be identical to any point on the torch body.
EDIT: I cant put up my source for the above numbers (lost itā¦ cant be bothered looking through my history) but a quick Google search should turn up something similar.
Itās OK, no source needed. Research shows some support for a difference, just no consistency on the amount of effect.
Flashlights are a special case, ano is needed. I would rather not see ano on interface materials, but improper removal could make things worse.
I say anyone who wants to de-anodize a light is doing it wrong, there are many examples of BLFers making their own lights but without the ability to anodize them
Absolutely right, but with one huge difference. The coolant liquid (or air) in an engine is pumped from the heat source to the heat exchanger, which also has a fan to improve airflow over the fins.
The whole thing is designed to move heat away from the engine in the most efficient way.
I sometimes think placing a large thermal mass against an LED emitter is a bit contrary to good thermal design principles. Once the heat soak is saturated, it holds heat there and becomes a heat trap.
Of course, if it can be radiated away quickly enough not to saturate then thats ok. Thin fins seem to get rid of heat better though. I think itās a function of surface area too. Of course, there is a tradeoff in robustness against efficiency here.
A CPU heatsink and fan might be the best possible design, but is more than a little impractical for most flashlights
Itās all design compromises. Ideally, all elements working together in an optimal manner will make a difference worth having.
Peltiers on LED stars anyone?