snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:
Try it. Take a red LED and a blue LED. Bright enough to read by. Both outputting the same amount of light, as judged by eye, when their beams are side by side on a white wall. Read some small print for a while, or walk around a dark cluttered room using them as torches. The red light won't reveal the detail with the same clarity. That's an extreme test but it will make the point. A more realistic test, dim an incandescent till you are a little above scotopic vision, but can still make out colour clearly, and read. Try the same again with a light that is strong in shortwave light, like a Cree LED lighting the wall beside you to get a diffuse light source. Eyes try to focus to improve visibility. They'll try harder to do that if they can't get enough shortwave light to make sharp details to focus on, if you're trying deliberately to use them to see that detail. Which is where the strain comes from.
That might not happen if you're not trying to look closely at anything, but many people consider reading a relaxing activity, and it isn't if you don't have enough shortwave light to render sharp text. If people weren't so conditioned to low colour temperatures, I think there might be less people with difficulty in reading as they get older. I don't know what research has been done on this but it could be interesting to see its results if any has.