Quote:
Originally Posted by gary
It would be interesting to hear of the relative improvement in
performing one of those Ishihara tests.
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I've tried a couple of the on-line Ishihara tests with and without the glasses. The results were modest at best, and inconclusive, if I'm honest - some numbers / patterns became slightly more discernible with the glasses, but most stayed pretty much the same. According to EnChroma, this is to be expected:
I took the test with the glasses: why didn’t my score improve?
Reducing the overall light level makes color vision tests more difficult. The EnChroma sunglass lens is generally considered too dark for use with a computer display, so one should not necessarily see an improvement in test score with the eyewear. When used outside in bright daylight, the reduced brightness does not have this potentially negative impact on color perception.
http://enchroma.com/faq/
It would be interesting to do a proper controlled Ishihara test using accurately printed samples under strong controlled light.
Note that a computer screen doesn't generate a true "white light" spectrum, being made up of only RGB pixels, so the rendering of the Ishihara tests can look subtly different on two different screens. The colour accuracy of digital screens varies depending on the filter pigments, screen technology (LED vs LED-backlit LCD vs OLED, etc). I suspect this is why some digital screens get a distinct green cast when viewed through these glasses, while others stay white.
If two Ishihara dots have almost the same true overall colour, but differ because one is missing a particular spectral element that my eye is not very sensitive to, then there would be no effective difference when viewed with or without the glasses. The glasses only change the perceived colour when they filter out a set of wavelengths that both the Red and Green receptors respond roughly equally to. By blocking that wavelength, the Red and Green receptors now get distinctly different filtered signals, instead of both being "swamped" by the intermediate "Red-Green" wavelengths.
As an extreme example, consider a screen where the Green pixels are all dead. White would be rendered exactly the same as Magenta (M = B + R), and putting on a pair of glasses which transmit 100% of Red and Blue but totally block the Green wouldn't help at all - filtering out a colour which isn't present in the original signal doesn't change the transmitted signal.