How can there be purple?

  • Thread starter hoodleehoo
  • Start date
How is there a color "wheel"? Color is just visible light on the EM spectrum which has red at one end and purple at the other end. But on the color wheel purple and red come back around and touch. How is that possible?

Purple just doesn't seem to make sense to me. Purple is blue and red light mixed (magenta might be the more accurate term), or if you just take the middle of the visible light spectrum (green) out of white. So, for blue to become violet, it'd have to start heading toward "red" again, which is on the other side of the visible light spectrum. How does it go toward red again? It just doesn't make sense to me.

I'm really racking my brain out here. lol
 

russ_watters

Mentor
18,650
4,882
How color is produced in nature and how it is perceived in the eye are two completely different and unrelated things. The color wheel is a representation of how your eyes generate colors, not how nature generates colors.

Strictly speakiing, light generated in nature doesn't have "color", it is just different wavelengths. Different animals percieve "color" differently because their eyes are adapted to process different wavelengths.

Also of note: purple and violet aren't quite the same thing - violet is a "spectral" color (it is part of the spectrum) whereas purple is generated by mixing. Here's the wiki on the subject: http://en.wikipedia.org/wiki/Violet_(color [Broken])
 
Last edited by a moderator:

DaveC426913

Gold Member
18,148
1,720
Ergo, when you're seeing purple, you're seeing more than one spectral colour. Or more accurately, you're getting both your red and blue receptors stimulated.
 
Thank you so much! You guys are awesome!

I wonder why our eyes opted to simulate violet with red and blue.
 

DaveC426913

Gold Member
18,148
1,720
Thank you so much! You guys are awesome!

I wonder why our eyes opted to simulate violet with red and blue.
You've got the question backwards. The question is:

I wonder why our eyes opted to show red and blue as violet.
 
Hmmm, now I'm confused. I thought we couldn't see violet so our eyes show it as red and blue?

"Spectral violet is outside the gamut of typical RGB color spaces, and although it can be approximated by that color shown below as electric violet, it cannot be reproduced exactly on a computer screen."

"Violet is a spectral color (approximately 380-420 nm), of a shorter wavelength than blue, while purple is a combination of red and blue or violet light.[7] The purples are colors that are not spectral colors – purples are extra-spectral colors. In fact, purple was not present on Newton's color wheel (which went directly from violet to red), though it is on modern ones, between red and violet. There is no such thing as the "wavelength of purple light"; it only exists as a combination.[3]"
 

DaveC426913

Gold Member
18,148
1,720
Hmmm, now I'm confused. I thought we couldn't see violet so our eyes show it as red and blue?
Violet light excites the blue receptors. Actually, http://en.wikipedia.org/wiki/Trichromatic_vision" [Broken]; it just excites the blue receptors the most.

Perhaps this is why we register violet as distinct from blue - our brain can tell the difference between
80%blue, 10%red (which might read as blue)
and
80%blue, 5%red (which might read as violet.)
 
Last edited by a moderator:
So violet is just an extreme blue? I though violet was more "purple" looking than blue so wouldn't it excite the red receptors more than blue would?
 
1,157
80
True violet has always been, as far as I can recall, the extreme blue end of the spectrum. When violet, or blue is mixed with red, then purple is obtained.

That's how I've understood it. Violet stimulates the blue receptors in our eyes. Purple stimulates both the red and blue receptors.

Unfortunately, many have interchanged the two as if they were synonymous, which they are not.

Claude
 

Related Threads for: How can there be purple?

Replies
12
Views
38K
Replies
34
Views
4K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top