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  1. #1

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    Are Red LED'S ok for red safe light ?

    There are a number of red LED's on the market now I have been wondering if anybody has tried them as a general purpose safe light ?

  2. #2

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    They use red LED's in the darkroom at Vraa-hoejskole (Denmark), and it is working OK....
    BUT I do not know the type.....

  3. #3

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    Hi !
    Yes, or no ;-)
    It depends on the LED. Some are emitting at the correct wavelength some don't.
    So if you want to try them, buy all from the same maker and test them for safety.
    Often, the salesclerk can't tell you either the maker nor the exact reference. They're just "red leds" for him....

  4. #4
    Lee L's Avatar
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    Many film and paper manufacturers post sensitivity curves. Most LED manufacturers also post emission curves. You could match that way. The problem is finding out which particular LEDs are in the product you buy. You could also just purchase your own LEDs of known make and emission curve and make your own safelight, very easy to do with a simple resistor and power source. I've used both red and amber LEDs in the darkroom for years without problems, and really like them. LEDs typically don't have a very wide spectral output.

    http://superbrightleds.com/images/spectral_graph.gif shows the output of the LEDs I use. Half-power spectral bandwidth appears to be about 25 nm with both the red and amber at recommended voltage/current.

    Lee

  5. #5
    Bob F.'s Avatar
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    By "LED" do you mean the commercially available LED based lamps? They do vary as suggested already, but they will be fine - it is not easy for an LED to emit very much light too far off its intended colour. Put it too close however and it will fog.

    If you make your own from quality LEDs and drive them at the correct current, out of band emission can be reduced to minimal levels allowing brighter light in theory than using bought lamps - but in practice I doubt it is worth the effort. Just do the usual safelight tests and you can certainly expect to end up with brighter light than the usual low-cost safelight with filters.

    I dislike red light (too gloomy) and use orange or amber LEDs in a home-made safelight. Unfortunately the only orange/amber ready-made LED lamp I could find locally emitted too much out of band to be useful (which just goes show how far you can take theory sometimes! )...

    Bob.
    Last edited by Bob F.; 11-05-2007 at 07:49 AM. Click to view previous post history. Reason: Syntax got messed up...

  6. #6

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    Lee..... what number do your LEDs have....?????

  7. #7

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    The easiest test is to expose your print paper to a set of LEDs, red or amber, to see if they expose the paper. When you find a light that doesn't, you've found the correct light for your situation.

    Granted that can be expensive if you have to buy all the lights, so as mentioned above, matching spectral sensitivity to spectral emission is the first step.
    When I grow up, I want to be a photographer.

    http://www.walterpcalahan.com/Photography/index.html

  8. #8
    Lee L's Avatar
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    Quote Originally Posted by Erik Hartmann View Post
    Lee..... what number do your LEDs have....?????
    Do you mean the product number from the website I mentioned in my post?

    If so, see this post: http://www.apug.org/forums/forum43/4...tml#post541132

    Much of hat thread is closely related to this one. Search APUG for "led safelight" and you'll come up with other useful ones.

    Lee

  9. #9

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    Bob,

    Would it be possible for you to put up on-line some kind of plan / design for your safelight?

    Tom.

    Edit) - Post 500; not exactly a major text in the field of photographic art and practice...

  10. #10
    Lee L's Avatar
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    This site: http://www.hebeiltd.com.cn/?p=zz.led...tor.calculator has a resistor calculator for LEDs in series or parallel. You need a DC power source (batteries or power supply), a resistor of the correct value, your LEDs, and a switch if you want to turn the LED off. As to the specific form the light takes, that's entirely up to the builder.

    Finding, buying, and shipping parts can get expensive if you source all the parts to build yourself. There are LED flashlight bulbs available in red (and perhaps yellow) or little portable battery powered arrays as seen here: http://superbrightleds.com/flashlights.htm that might be cheaper and just as useful as home-built. You could just slip a red LED into a flashlight and bounce it off the ceiling, or grab it an point it where you need it at the moment.

    Lee

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