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In the past when I have used a darkroom the safe lights have been a dim incandescent bulb, with an 'orangish' colored filter.

Given red light is less energetic than orange, and LEDs are reasonably monochromatic, can they (e.g., a bike rear clip on light) be used as (cheap) darkroom safe light?

  • FYI – John Apr 20 at 8:31
  • Please specify if you'll only be working with monochrome (B&W) film, and if so, what specific types. Different monochrome films can be more or less sensitive at different wavelengths than other films. Ditto with the paper you plan to use. For color film/papers, the options are much more limited (pretty much zero for conventional color imaging). – Michael C Apr 21 at 5:42
  • @MichaelC There are few to no B/W film emulsions now which can be used with any kind of safe light. On the other hand there are few to no B/W papers which can't. (I think there are some non-panchromatic films, I doubt there are any panchromatic papers as they would be so horrible to work with.) – tfb Apr 21 at 9:16
  • @tfb The main point is that the question doesn't even make clear if the OP is concerned with monochrome/B&W or color. Certain assumptions need to be made clear. – Michael C Apr 21 at 10:37
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    @John Please don't leave mystery links without explanation. – mattdm Apr 21 at 13:02
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Yes, they can. The darkroom I work in uses the strips of red LEDs you can get to put in car rear windows, all run from a 12 volt supply, as safelights and they work brilliantly. I believe that fairly extensive tests were done before I joined: leaving paper out for hours & then checking for fogging. I'd encourage anyone planning on doing this to do similar tests, but they work very well.

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Before making assumptions on monochromaticity with LED lights that aren't built for this purpose, test and/or measure. LEDs are often overdriven, and/or allowed to get reasonably hot, and/or used in pulsed modes in these applications. All this can affect their spectral behaviour (compared to datasheet values) a lot.

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Beware of red LEDs that are based on blue LED chips + red phosphor, they may still emit a fair amount of blue light. I don't know how many there are out there, just saying.

Same for amber/yellow LEDs, they may be fantastic, or they may be useless.

https://www.google.com/search?q=led+darkroom+safelight = 42100 results.

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