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Following the question:

Sensitivity of eye

I would like to make sure what these % says about? Is it the ability to colour detection?

enter image description here The similar stuff is here: http://www.giangrandi.ch/optics/eye/eye.shtml

But I am not sure, what meams human eye sensisitivity at 1 or 0. Could somebody explain?

Thanks & Regards,

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  • $\begingroup$ It is not possible for anybody to understand the question without following the link, but links do not always remain valid. Could you please include a brief description of what you saw on that page? (P.S., I saw the word, "relative," and I think that word may be pertinent.) $\endgroup$
    – Solomon Slow
    Commented Dec 12, 2019 at 14:28
  • $\begingroup$ I have added pic already. I mean the percentage on the vertical axis. $\endgroup$
    – Geographos
    Commented Dec 12, 2019 at 14:44

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The curve you see is a plot of the photopic luminosity function.

If you look at two same-size spots of light with the same power in each, but differing by wavelength, their brightnesses will differ. E.g. if you shine a 405 nm laser pointer at a white wall, and a 532 nm pointer of the same power (e.g. 1 mW) near it, you'll notice that the spot of the former seems duller than that of the latter, despite the power being the same. Moreover, if you try the same experiment with e.g. 1 mW of 808 nm laser pointer, you'll most likely not even notice the spot, except when looking at the reflection at a special angle in a dark room.

The luminosity function is a way to quantify these "amounts of visibility" of different wavelengths. It appears that the human eye in photopic (daylight) vision mode is most sensitive to 555 nm light, and the sensitivity decreases away from this wavelength. This is reflected in the maximum of the photopic luminosity function.

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It basically means that the eye can see the difference between two light sources of similar brightness V(λ) times worse than for the best wavelength at moderately bright levels, or the eye is V'(λ) times worse in detecting light at all in the darkness (low-light, scotopic).

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  • $\begingroup$ So if the value is for instance 50%, then I can see 50% less of the object color? $\endgroup$
    – Geographos
    Commented Dec 12, 2019 at 14:57
  • $\begingroup$ Not exactly. Color and wavelength are different species. For instance, we see the spectrum on the plot you put here. Almost none of the colors you see is represented by a monochromatic wavelength it tries to imitate. Monitors are adjusted to the human eye tri-color sensitivity. 50% of bright sensitivity means that in equal conditions the eye sees changes in brightness two times worse. For example, you could see difference between 1.00 and 1.01 brightness of green on the verge of sensitivity. 1.008 is perceived as 1.00. Then, cyan can be seen as different only at 1.02 level. $\endgroup$
    – Philipp Oleynik
    Commented Dec 13, 2019 at 10:53

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