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  1. #11
    glbeas's Avatar
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    Quote Originally Posted by efikim
    ... and I've remembered where I found the reflectances (in a book on building greenhouses).

    I remembered it wrong, so my apologies!

    white paint reflectance 80-90%
    glass mirror 80-90%
    polished aluminium 60-70%
    aluminium paint 60-70%
    stainless steel 55-65%
    Thanks for the info, any idea what polished chrome would be?

  2. #12

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    No, that's all the book has; sorry.

  3. #13
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    Polished chrome would probably be a bad idea because it is too specular and would make your exposures uneven. Any specular surface would most likely do the same because of the inverse square law. Best to use something more diffuse. If you are using multiiple tubes you should have plenty of UV anyway.
    Pity the dyslexic agnostic insomniac who lies awake night after night wondering if there is a dog.

  4. #14

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    I checked the Edmund Industrial Optics catalog, in the mirror section. The aluminum coatings are the most efficient at UV, down to about 350nm. Gold was worst, dropping off sharply below 650nm. These are all for first surface mirrors, since as others have pointed out normal glass absorbs UV. Their UV lenses are made from "fused silica". They used to sell a white reflective coating paint, but I couldn't find it in their catalog. That would be your best solution, since it would diffuse as well as reflecting it. I think you would have too many hot spots with a mirror. If you want to go the mirror route, get a standard first surface mirror and don't worry about exotic coatings. I bought an 8x10" piece once from a glass store, they sold it for people who build kaleidoscopes (so it was cheaper than a "scientific" mirror :-)

  5. #15

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    The information posted here about reflection of light from certain surfaces has been quite interesting. However, to return to the original question that prompted the thread, I agree with Mike Finley's first response, i.e. a coating of white paint on the inside of a UV bank of tubes would be more effecteive than mirrors, and probably about as effective as any other coating.

    I have made and used a number of UV tube banks. Initially the issue of internal reflection was a subject of considerable interest for me. Eventually what I found was that it makes virtually no difference at all whether you provide internal reflection or not, and i f so plain white paint is as good as anything. However, even if you just leave the inside unpainted (assuming it is a light wood wuch as pine or fir) I seriously doubt that you would be able to detect any loss of printing speed compared to any other reflection method you devise.

  6. #16

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    I just remembered Ed Buffaloe's excellent site, www.unblinkingeye.com. Check the article from Sandy King on building a UV source:
    http://unblinkingeye.com/Articles/Light/light.html
    I gave it a quick glance and didn't see any mention of reflectors behind the tubes.

  7. #17

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    Thanks everybody for sharing all that you know. Thanks to Sandy for bringing the practical answer into the thread. This is good news that plain white paint is as good as anything else. I really did not want to get into attempting to line the box with mirror like material.

    As an aside.....

    I caught Sandy's answer to a question on ABC Pyro on Tuan's site. I just want to say that we are indeed blessed not only to have Sandy's wealth of knowledge shared here, but the crown jewel is that he has the wisdom and maturity to temper his responses with a great deal of practical common sense.

    A personal trait I fear that is often sorely lacking from some of the answers I have seen throughout the years. (of course nobody here comes to mind) I cannot sing my praises loud enough in respect for Sandy and how an answer like that has moved him very high on the ladder in regards to being listened to and believed when he offers a candiate opinion.

    Kind Regards,
    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

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