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Thread: Why do flashlight get anodized?

  1. #1
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    Default Why do flashlight get anodized?

    I was wondering what the purpose of anodizing aluminum flashlights is. AFAIK aluminum doesn't get attacked by water or air (doesn't rust and doesn't develop any kind of patina) so... why do we need aluminum flashlights to be anodized (any type and color of anodizing)? Do we need it in the first place?
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  2. #2

    Default Re: Why do flashlight get anodized?

    It isn't strictly needed; there are plenty of plain aluminum lights out there doing just fine. Anodizing increases durability and helps with aesthetics. Also it is sometimes it is used to block electrical path through threads so that loosening the threads causes mechanical lockout.

    Also aluminum can definitely corrode, just take a look at Land Rovers from the 60s. Not really relevant to flashlights though, unless it's a dive light.
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    Flashaholic* thermal guy's Avatar
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    Default Re: Why do flashlight get anodized?

    One reason is the looks. Ever seen a stripped aluminium light? Some like the looks but definitely not my style.
    If i had one day left to live i would want to be at my workplace.Because every day is like a frickin eternity.

  4. #4

    Default Re: Why do flashlight get anodized?

    That's one of those questions that causes some to say "hhmmmm"....
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    Flashaholic* Timothybil's Avatar
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    Default Re: Why do flashlight get anodized?

    It's my understanding that it also protects from dings and scratches. That is why you will see peo0ple making a distinction between HA II and HA III anodizing, with HA III being stronger. Also, it is practically the on ly way to apply color to an aluminum light. One could paint it, but paint can rub or flake off a lot easier than anodizing does.
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    Default Re: Why do flashlight get anodized?

    Powder coating metals is usually cheaper, but sits on the surface and rubs off with wear. Anodizing embeds color deeper into the actual metal and is significantly more durable to keep it's color even when scratched. I also find that anodizing is less prone to leaving fingerprints. Shiny surfaces are nice when kept clean...

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    Flashaholic* Timothybil's Avatar
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    Default Re: Why do flashlight get anodized?

    New question. What exactly is ceracoating, and where does it fit in this discussion?
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    Flashaholic* Thetasigma's Avatar
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    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by Timothybil View Post
    New question. What exactly is ceracoating, and where does it fit in this discussion?
    Assuming correctly done anodizing and cerakote.
    Where anodizing is an electrochemical process to produce a controlled oxidation of the aluminum to generate a very durable layer of aluminum oxide that is chemically bonded to the aluminum, cerakote is a ceramic based finish that is carefully applied to the part to be finished. Cerakote is essentially a paint so it is only as impact resistant as its base material, in this case aluminum is somewhat easy to flake cerakote off on impact. Cerakote IMO makes more sense on firearms or steel parts where the base material is harder than say an aluminum light.

    As for general comparison, anodizing can be more durable to wear and impact but especially the stronger HA type III, is quite limited in what sort of colors you can get. Cerakote while less durable has a plethora of color options available, for example you could get a pink and zombie green on the same light if you really wanted to, anodizing is going to be a singular color as it is colored by dyes in the chemical bath entering the pores and being sealed in.
    Last edited by Thetasigma; 05-16-2019 at 12:07 PM.

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    Administrator Kestrel's Avatar
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    Default Re: Why do flashlight get anodized?

    My apologies for the interjection of a clarification; there are no such things as HA II or HA III.

    There is Type II anodizing; Type III is also called HA.

    HA-III is sort of like saying Roger-Roger or Pizza Pizza.

  10. #10

    Default Re: Why do flashlight get anodized?

    I like black type lll HA personally because of the way it looks. There is going to be differences even among the type lll HA's though. From Surefire to Elzetta to Malkoff, they all differ. I like Malkoff the best myself, but some old 6p's are very nice too. Does one "need" an anodized light? Maybe not. Depends what you like and what your doing with the light. If you get a colored Elzetta Limited Edition light, they are first anodized type lll HA then ceracoated over the top of that.

  11. #11
    Flashaholic* thermal guy's Avatar
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    Default Re: Why do flashlight get anodized?

    I donít even think any but the cheaper lights use type II.i plasma coat for a living and have always wanted to coat one of my lights. Problem is thermal spray doesnít take to well to impact. As far as wear. They do not ever wear. Not with hand use anyways
    If i had one day left to live i would want to be at my workplace.Because every day is like a frickin eternity.

  12. #12

    Default Re: Why do flashlight get anodized?

    There is also the PVD process that could be construed as similar to powder coat or cerekote where the coating is in a gasious state and electrically bonded to an electroplate of material(s) over the alluminum. Foursevens blue Paladin and PK's PR-1 used that process.
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    Default Re: Why do flashlight get anodized?

    Aluminium does corrode. If you own a alu boat, and dont change zinc anodes, well the boat will sink Also i dont consider bare alu as clean, put bare alu in your pocket, and your pocket will turn black over time. if you rub bare alu at a white wall, it will leave a mark, just like a pencil.

  14. #14

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by thermal guy View Post
    One reason is the looks. Ever seen a stripped aluminium light? Some like the looks but definitely not my style.
    Oh...I don't know.




  15. #15

    Default Re: Why do flashlight get anodized?

    So far so good.



    Last edited by bykfixer; 05-16-2019 at 04:43 PM.
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    Flashaholic* Thetasigma's Avatar
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    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by Kestrel View Post
    My apologies for the interjection of a clarification; there are no such things as HA II or HA III.

    There is Type II anodizing; Type III is also called HA.

    HA-III is sort of like saying Roger-Roger or Pizza Pizza.
    Thanks for the clarification.

  17. #17

    Default Re: Why do flashlight get anodized?

    Bare aluminum will turn your hands black if you handle it a lot. Anodize is very durable and while you need to get it off of electrical contact surfaces because it's non-conductive it improves the thermal conductivity of aluminum. That's never a bad thing on a modern light.

  18. #18

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by focusworks View Post
    Bare aluminum will turn your hands black if you handle it a lot. Anodize is very durable and while you need to get it off of electrical contact surfaces because it's non-conductive it improves the thermal conductivity of aluminum. That's never a bad thing on a modern light.
    This last bit is most interesting. Would you mind elaborating on it? How does it improve the thermal conductivity?

  19. #19

    Default Re: Why do flashlight get anodized?

    There is also the aesthetic value of anodizing. Look up tjís custom gunworks to see some of his work with anodizing
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  20. #20

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by Skaaphaas View Post
    This last bit is most interesting. Would you mind elaborating on it? How does it improve the thermal conductivity?
    No blanket on the outside. The anodize coating could act as a thin layer of insulation. I say could because some desingers build their ideas around the properties of the annodize layer to achive a more efficient conduit.
    Last edited by bykfixer; 05-18-2019 at 08:24 AM.
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  21. #21
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    Default Re: Why do flashlight get anodized?

    Anodizing done in batch processing is extremely cheap to perform.

    The military process Mil-A- 8625 type III is typically a natural color finish which varies from tan to olive green. Black anodizing is a dye added to the sealing operation.

    Type III anodizing is a minimum of .002Ē thick and is done for abrasion resistance first, then corrosion resistance secondly. .002Ē doesnít sound like a lot of thickness, but thatís per surface, so threads arenít the best thing for type III.

    As for Ceracote, iíd do KG Coatings Gunkote instead. Can be performed at home and if you select the 1000 series material, itís room temperature cured.

    Lauer Firearms offers a coating called Duracote. Duracote is Sherwin Williams Polane repackaged at five times the cost.
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  22. #22

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by bykfixer View Post
    No blanket on the outside. The anodize coating could act as a thin layer of insulation. I say could because some desingers build their ideas around the properties of the annodize layer to achive a more efficient conduit.

    Black anodized aluminum has significantly better emissivity than bare aluminum and better than oxidized aluminum hence it will run cooler ... It dissipates more heat.

  23. #23
    Administrator Kestrel's Avatar
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    Default Re: Why do flashlight get anodized?

    The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

    Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.

    And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
    1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
    2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

    And yes, this is my field of study

  24. #24

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by Kestrel View Post
    The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

    Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.

    And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
    1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
    2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

    And yes, this is my field of study
    Woosh :-)

    Thanks for the answer, gave me a lot of stuff to go Google!

  25. #25

    Default Re: Why do flashlight get anodized?

    Quote Originally Posted by Kestrel View Post
    The issue with that reasoning is that while heat loss by radiation is to the fourth power of delta-T (compared to the third power of delta-T for heat conduction or convection) the radiative coefficient is far far smaller, so that aspect is relatively insignificant until delta-T is in the ~500+ Kelvin region.

    Short version: for 'normal' temps relatively close to ambient, thermal radiation can be ignored for calculating overall thermal transport.
    While your analysis sounds impressive and you are correct that conductive heat loss, especially if hand held is dominant, heat-loss due to radiation while low, is not necessarily insignificant, when one considers the use case and the failure mechanisms for both LEDs and the electronics associated with them. True, for a handheld light that is use maybe a few 100 hours, it won't matter, but even for flashlight users, there are usage models where the difference is substantial ....

    q = ε σ (Th4 - Tc4) Ah

    Plug some real numbers ....

    σ = 5.6703 10-8
    ε = 0.8
    Th = 333.15 (60C - cause you tail standed on a table to light a room)
    Tc = 288.15 (15C - rooms a bit cool, but maybe you are outdoors and that number becomes lower)
    Ah = 0.015 = 3cm diameter, 15cm length -- It's a bit of a bigger flashlight, but still quite reasonable for a higher powered unit.

    Total Radiative Heat loss = approx 3.5 watt


    Assuming that flashlight is sitting is tail-standing on a table, the heat loss due to convection is going to be pretty poor. The heat loss due to convection and radiation are going to be pretty similar, i.e. +/-50%. Since this is your area of study ... I am sure you can do the math yourself.

    Now, with the emissivity of oxidized aluminum from 0.1 - 0.2, and the emissivity of anodized aluminum being 0.7-0.8, one can see quite clearly for this larger flashlight, the heat loss difference between anodized and non-anodized would be almost 3 watts. THAT is not insignificant.

    For a 7W total heat loss (10 watt flashlight, LED efficiency low due to high drive, optic and electrical losses), the difference in operating temperature between 0.2 and 0.8 emissivity for our tail stander is going to be 10-20 celsius different. That is not insubstantial.


    Quote Originally Posted by Kestrel View Post
    And for those admiring the 270W/mK thermal conductivity cited for single-crystal alumina compared to the high-300's for polycrystalline aluminum metal, please keep in mind the two following issues:
    1) Thermal transport between adjacent grains of Al2O3 is very low due to poor phonon coupling.
    2) Thermal transport between Al2O3 and aluminum metal is also very low due to inefficient coupling between electrical and phonon heat transfer.

    And yes, this is my field of study
    Not sure what relevant point you are trying to make? A higher number, i.e. high 300's versus 270, would mean that the polycrystalline aluminum would be a better conductor than single crystal alumina, but both these numbers are wrong. Aluminum is typically about 237, not high 300's, and single crystal alumina, i.e. sapphire for the less informed, is about 35-40.

    https://www.azom.com/properties.aspx?ArticleID=1721
    Last edited by MeMeMe; 05-19-2019 at 06:04 PM.

  26. #26
    Administrator Kestrel's Avatar
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    Default Re: Why do flashlight get anodized?

    Ok, yes it is easier to get accurate numbers when looking up references; I happened to recall the TC for Aluminum Nitride rather than for Aluminum Oxide.

    I did note your analysis stopped short of calculating heat flux - '10/20 deg cooler' doesn't appear to be a complete answer to the original query. Comparing heat radiation to convection during tailstanding is less relevant than holding the flashlight in the hand - i.e. conduction - which is closer to common configs, and helps keep flashlights significally cooler than from the contribution of heat radiation.

    Not sure what relevant point you are trying to make?
    If you were to bother with reading prior posts, you would see that component of my reply was to content from another poster rather than yourself - sorry to let you know that this thread isn't about you in it's entirety.

    I'm just too busy to dig into the weeds with technical pissing contests, which is why I try to avoid posting in these threads. Please feel free to continue using 'The Google' for informing others here.

    Best regards,
    Last edited by Kestrel; 05-19-2019 at 06:38 PM.

  27. #27
    Flashaholic* thermal guy's Avatar
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    Default Re: Why do flashlight get anodized?

    Lots of numbers folks. Lots of numbers. Anodizing makes the light pretty. Letís leave it at that😂😂😂
    If i had one day left to live i would want to be at my workplace.Because every day is like a frickin eternity.

  28. #28

    Default Re: Why do flashlight get anodized?

    Way over my head.

    I surmize that some anodize for a thermal benefits?
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  29. #29
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    Default Re: Why do flashlight get anodized?

    Photons, phonons ... let's not get over-excited, they're all just wavicles to me
    ... is the archimedes peak

  30. #30

    Default Re: Why do flashlight get anodized?

    ... or you could admit you were inaccurate and that yes I deed anodizing makes a difference. The 10-20c was from a quick simulation I ran. Too many variables to nail down a number so 10-20 felt honest. 20 is very realistic for the scenario given. It's my line of work too.

    I provided a reference in case their was a question of my accuracy. It's best when telling someone else they are wrong and it is their area of study.

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