Talk:Safelight

History

For some interesting historical info re safe lights see this book available on Google Books. --Una Smith (talk) 05:03, 31 May 2008 (UTC)

Green light?

A cannister of ORWO b&w movie film says "open only under green light".

this is the label (see middle right of the image)

Why would green be a safe light? I have been able to find absolutely no explanation of this anywhere on the internet... BigSteve (talk) 12:00, 24 October 2012 (UTC)

@Bigzteve: Very belatedly: green of a certain hue was also the safelight recommended for use with many early panchromatic black-and-white emulsions, including those on Autochrome color plates (1907-1930s)—that is, if the darkroom worker found operating in total darkness (always the only truly safe "safelight") intolerable. The explanation is that although such emulsions are much less sensitive to deep red than to any shade of green, they do have a region of low sensitivity around the middle-green part of the spectrum, while the normal human eye is most sensitive to greenish-yellow light, but its sensitivity to red, like the emulsion's, drops off to nil at the far red end of the spectrum (nearing which, unless dazzlingly intense, all wavelengths of red appear to be the same color, just increasingly dim). Given a red and a green light source balanced so that each will just barely fog the film after n seconds of direct exposure at a distance of n feet, the green one will seem much brighter to the human eye and can therefore either provide a visually much brighter darkroom, or be swapped for another of lower wattage to provide an apparent brightness equal to the red light combined with a much longer safe exposure time. However, it may be the case that light of a far red wavelength, still visible to the human eye but having for all practical purposes no effect on the emulsion, could in theory provide a light very safe for the film yet sufficiently high-powered to seem as bright as a green or at least an ordinary red safelight, but that would require the use of a very narrow-band light source, such as a laser of substantially longer wavelength than a typical red laser pointer, and frequent or prolonged use might be harmful to irreplaceable eyeballs. 66.249.174.212 (talk) 11:00, 4 September 2016 (UTC)

Many black and white panchromatic films have a note that a Green (Wratten 3) filter can be used half way through development. The idea behind this, is that the sensitizing dyes have mostly washed away by then. And also, that green is the peak of the human sensitivity. This allows one to increase or decrease development time, based on the image. I have never tried this. I suspect it takes some practice. Gah4 (talk) 05:16, 18 October 2024 (UTC)

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