It is true that to make vivid violet that can easily be seen by humans,
mixing in a little red with blue helps.  But it is not true that you
must do this to achieve the color violet.  There is a part of the
visible spectrum  that is monochromatic violet, around 400 nano or so.
It's not strongly visible, but it is visible to the normal human eye as
violet without any red light at all.

w.stacy, o.d.

On 1/15/07 12:34 AM, in article
1168850061.166511.59230@m58g2000cwm.googlegroups.com, "David Jonsson"
<davidjonssonsweden@gmail.com> wrote:

Even the excellent Wickipedia article leaves some things out.

Not long after diode lasers were first announced, some laser diodes were
made where I worked. While I do not remember their wavelength it was
somewhere near 860nm well past the end of the graphs presented in the
references above.

These diodes had to operated cold at liquid hydrogen temperatures. With a
dark adapted eye, we could look into the dewar to see dim flashes of light
from the laser. The laser HAD to be pulsed to reach threshold. The
impression was that of orange light. My guess is that the tails of the
responses, small as they are, extend well into the near infrared. The orange
color indicates that least two sets of cones respond.

The same extended low level response at long wavelengths is also present in
photomultiplier cathodes. Of the old line photo-surfaces, only the S-1
material had published response to neodymium radiation at 1.06µm.
Nevertheless, there were some photo-surfaces that were responding weakly to
the neodymium radiation.

Bill
-- Fermez le Bush