Biology Reference
In-Depth Information
11
Night vision may appear bluish
The origin of the idea that rods may give rise to chromatic sensations
may be traced back to the hypothesis of Ebbinghaus (
1893
) that the
photopigment of rods (rhodopsin) was the yellow-blue see-substance
postulated by Hering (
1878
), and the suggestion of König (
1894
) that
the rod receptors represented the primary 'blue' receptor system
of photopic vision. Substantial evidence in favour of the idea was
provided by von Kries and Nagel (
1896
) who found that twilight
vision contained a tint of blue.
In order to identify more precisely this blue colour quality of
rods, von Kries (
1896
) attempted to find the spectral light that did
not change its hue when test intensity was reduced from photopic to
scotopic levels, i.e. when the rod component increased. He used Nagel
(a deutranope) as his subject and instructed him first to make a colour
match at a photopic intensity level between a homogeneous spectral
test light from the short-wave region of the spectrum (and hence with
a relatively high potential scotopic value) and a mixture of spectrum
red (670 nm) and violet (435 nm) lights (and hence with a relatively
low potential scotopic value). Thereafter, the intensity of the test
and comparison fields was reduced in the same proportion from the
photopic level until the homogeneous light strongly activated the
rod component. His results showed that the spectral light that did
not change in colour quality with intensity reduction was situated
between 480-485 nm, i.e. in the green-blue part of the spectrum.
Dreher (
1912
) made a somewhat similar investigation using
two trichromats as subjects and confirmed the results of von Kries.
G. E. Müller (
1923
), in his review on the colour quality of night vision,
also concluded that, in addition to the dominant achromatic component,
it entailed a tint of green-blue. He presumed that this green-blue colour
