doesn't even have to be three,
look up tetrachromacy.

also, oddly, there's no way to make violet using red, green and blue, you can only closely approximate it. apparently.
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 21:50, archived)

Which is strange
as it's detected by a balance of red and blue sensors in your eyes.

I've heard this before though. I don't understand it.
( Flapjack I spay a little mare for you, Sun 14 Jun 2009, 21:52, archived)

no,
me neither.
it must be something to do with the sensors detecting a frequency band, rather than a single wavelength. maybe the bandwidth is so variable that violet looks different to everyone, so there's no single combination of red and blue that looks right to more than a small number of people.
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 21:53, archived)

en.wikipedia.org/wiki/Purple#Purple_versus_violet

It's a relative lighting thing, it seems.
( Flapjack I spay a little mare for you, Sun 14 Jun 2009, 21:54, archived)

No, wait, it's OK
it's just that purple doesn't exist.
( Flapjack I spay a little mare for you, Sun 14 Jun 2009, 21:56, archived)

purple exists,
just like white exists, it's just not a single wavelength on the spectrum.
Actually no colour you ever see in nature is just a single wavelength.
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 21:58, archived)

Are you telling me these streetlights didn't sprout here?

( Flapjack I spay a little mare for you, Sun 14 Jun 2009, 22:02, archived)

they have a sharp wavelength peak,
but they'll have a continuous spectrum superimposed on that as well. I think.
Any light coming from them will no doubt have been affected by other things by the time it hits your retina anyway.
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 22:05, archived)

the spectrum of a sodium street lamp apparently looks like this:
www.chemistryland.com/CHM107Lab/Exp7/Spectroscope/SodiumLamp500.jpg
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 22:13, archived)

i'd love to get my hands on some streetlamp beans
imagine the fun you could have planting them in neighbours' gardens, or sneaking them into pot plants belonging to people you didn't like

or eating them! what'd that be like?

i'd swap my only cow for three of those beans
( spacefish bong!, Sun 14 Jun 2009, 22:09, archived)

Interesting.
Silly trichromat!
( The Doveston haunted by the memory of his own amnesia, Sun 14 Jun 2009, 21:57, archived)