Hello,
I know the history behind the selection of traffic light colors, but I want to know if these colors were selected because of their diffraction and the distance they are visible.
There are conflicting stories given for the reason red lights are used to indicate stops. One is the posibility that red lights can be seen as red from the furthest distance, and the other is that red has a long-standing association with warnings or danger. Some possibly interesting historical links are:
https://books.google.com/books?id=ZtY-AQAAMAAJ&dq=rail%20%22red%20signal%20light%22&pg=PA130#v=onepage&q=rail%20%22red%20signal%20light%22&f=false
https://books.google.com/books?id=Z6NJAQAAMAAJ&dq=%22red%20means%20danger%22&pg=RA2-PA121#v=onepage&q=%22red%20means%20danger%22&f=false
At this point in time the practice of using red lights to indicate stopping is so universal and widespread across so many disciplines and modes of transportation that it is unclear (to me) whether red truly had a connotation of danger/warning before red signal lights were used, or whether this association came about because of this universal practice. it is certainly an interesting question for Ihistorical research!
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