🚀 go-pugleaf

Pardon me for not editing the newsgroups line,
but I couldn't decide to which newsgroup this digression
was less relevant.

From article <255@rna.UUCP>, by dan@rna.UUCP (Dan Ts'o):

> 	As far as why your blue LED appears purplish. It probably is
> psychophysical/physiological, rather than any red output.

agreed

> Just as the
> extreme shortwavelength end of the rainbow appears violet/purple, the
> blue LED probably is emitting light at, say 430nm.

OK

> Your red cones in the
> retina actually have significant sensitivity in the deep blue region --
> more so than your green cones.

certainly not (reference upon request)

> Thus deep blue appears purplish or
> actually bluish/red, an anomolous sensation.
                          ?????????

The shortest visible wavelengths are usually referred to as "violet"
(that's why the slightly shorter invisible wavelengths are "ultraviolet").
Psychologically unique "blue" (that which appears neither reddish
nor greenish) is evoked by somewhat longer wavelengths (without
looking it up, I'd guess about 480 or 490nm).  A light increment
(away from white) affecting only the blue-sensitive cones
will appear violet, while the corresponding decrement appears
chartreuse (greenish-yellow).  The commonly accepted
physiological explanation for this is that the signal from
the "blue" cones combines with signals from the "red" cones
in the formation of a red-green opponent signal in the brain.

-- 

	Jeff Mulligan (jbm@aurora.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-6290