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(meteorobs) Colour perception
Guys -
The following is a cross-posting from our Canadian RASClist, a question that was
posted on colour perception, answered by a friend of mine. It impacts on various
types of astronomical observing. Thought you might be interested...
- Cathy
Great White North
______________________________________________________________
> Back to reality (such as it is), a question for you then. How would
> red-green colour blindness affect or be affected then by different
> wavelengths of light, if at all? Any research on that topic?
There are two forms of red-green "colour blindness" which are due to a
loss of spectral sensitivity of the retina to either long or mid-range
wavelengths of visible light. When the loss is in the long (red)
wavelengths, we call it a protan defect; a loss in the mid-range (green)
is a deutan defect. For the protan observer, shades of red are generally
seen as shades of grey or "muddy" reds, while the deutan observer sees
shades of green either as grey or washed out greens. Other hues are
distorted relative to normal colour perception as well. The most severe
forms of defective R/G colour vision are protanopia and deuteranopia. In
these conditions, there is very poor discrimination of reds and greens,
and we find that certain hues are confused because they look the same to
these observers. Tests of colour vision such as the Ishihara
pseudo-isochromatic plates (the coloured dots with numbers in them) take
advantage of this colour confusion so that the exact type and degree of
colour vision defect is identified. There is a lot of visual science
literature on the subject - it dates back to the first report of
defective colour vision by the English scientist John Dalton. About 8%
of males and 1% of females have defective colour vision.
In our work here at Waterloo, my research group on visual and ophthalmic
standards does quite a lot of consulting and resarch work on industrial
and visual safety standards, including the visibility of coloured
information panels and signal lamps for normal and defective colour
vision. It is quite an important problem.
As far as visibility of colours is concerned, an observer with either
type of defective colour vision will have difficulty with both
identification and discrimination of various colours. Colour naming is a
problem, as is the luminosity. For example, consider a very red star
like Mira. We normal colour observers see a fairly bright, deep red
object in the telescope. For someone with a severe protan defect, Mira is
going to appear much fainter because the cone receptors will not respond
to the red light of the star. On the other hand, a bright white star
like Vega will not appear much different because of the different
spectral distribution of the light: much more short wavelength light
where the protan has near normal sensitivity.
BTW, there is some suspicion that long-term visual observers of variable
stars may show a slight shift in their observations of brightness and
colour of stars due to the development of cataract and other eye
conditions that can affect colour vision. The AAVSO database of visual
and photoelectric photometric observations of bright variable stars
should be a gold mine for such a study if it could ever be funded.
B. Ralph Chou, MSc, OD
Associate Professor
School of Optometry, University of Waterloo
Waterloo, Ontario, Canada N2L 3G1
Tel: 519-888-4567x3741 Fax: 519-725-0784
e-mail: bchou@sciborg.uwaterloodot ca
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