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A friend of mine who is (completely) red/green color blind once told me that he can distinguish the green traffic light from the yellow and red one despite his color blindness and that he thinks to be able to remember having heard that this is not an accident. Is there some law or guideline for it or is it just niceness on the traffic light manufacturer's part and what exact green is it?

In case it matters, I'm living in Germany.

(Sorry, if this is the wrong SE; it seemed like the most appropriate one.)

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  • $\begingroup$ There really is no such thing as an exact green. It depends on how you are measuring it. Different people will see the same color differently. $\endgroup$
    – Eric S
    Commented Nov 20, 2022 at 17:14
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    $\begingroup$ in my city the color varies between different models of the traffic lights $\endgroup$
    – jsotola
    Commented Nov 20, 2022 at 18:42
  • $\begingroup$ With "exact green" I mean something like wave length or important characteristics that a "green" color needs to posses, so that a color blind person can distinguish it. $\endgroup$
    – zvavybir
    Commented Nov 20, 2022 at 18:49
  • $\begingroup$ @jsotola Are you living in Germany? $\endgroup$
    – zvavybir
    Commented Nov 20, 2022 at 18:50
  • $\begingroup$ @ErnestBredar no I am not $\endgroup$
    – jsotola
    Commented Nov 20, 2022 at 18:51

2 Answers 2

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I am red-green color blind. I researched and blogged about this years ago. Since then, the primary sources have disappeared off the internet, except for the official CIE standard, which is expensive. So unfortunately you may have to take my word for it.

Green traffic lights are are slightly toward the blue end of the spectrum, which lets people like me differentiate them from red lights. There is some variation in the allowed color range, but they are all distinct from the pure green that's hardest to tell from pure red.

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  • $\begingroup$ Thanks a lot!! I had this question for ages, so nice to finally have an answer! $\endgroup$
    – zvavybir
    Commented Jul 19, 2023 at 2:48
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Red-green color blindness is a reduced ability to see color. It's not total. Traffic lights are not all the same color. LED and incandescent traffic lights look slightly different.

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  • $\begingroup$ There appears to be a translation problem. With "color blind" I (and he) mean complete inability to distinguish red and green. About your other point with the different colors: That just means that it appears to be either a more widespread phenomenon or that today here (quasi) all incandescent lights are phased out, not that my question is unanswerable. $\endgroup$
    – zvavybir
    Commented Nov 21, 2022 at 17:28

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