Are Violet and Purple the Same Thing?
Violet is just another word for purple, right? Not quite. The colors may look the same, but in terms of physics, they're totally different. Our eyes have three types of color-sensitive cells, or cones, each specialized to one color: red, green, and blue. These colors lie in order on the visible light spectrum. Despite their specialization, the cones generally combine their forces and activate in the presence of more than one color. Green and orange, for example, both activate the red and green cones, but in different ratios. Violet activates the blue cones in abundance and the red cones a little less. Of course, not all colors are in the light spectrum as we know it: brown, for instance, is not a spectral color, but a combination of many different colors on the spectrum. When you see brown, you're seeing a mixture of light wavelengths that activate different cones in varying ratios to produce a color your brain finally interprets as brown. This is how we see purple: it's a combination of the spectral colors blue and red. Rather than activating blue and red cones in a given ratio, purple combines the cone ratio for blue with the cone ratio for red to come up with an entirely new color.
from Crash Course
Key Facts In This Video
Nearly 70% of all the sensory receptors in your whole body are in your eyes. Nearly half of the cerebral cortex is involved in vision. (0:48)
Light hits your posterior retina and spreads from the photoreceptors to the polar cells to the innermost ganglion cells. The ganglion cells form the optic nerve, which carries visual impulses to the thalamus and onto the brain's visual cortex. (5:43)
Cones detect fine detail and color, and can be divided into red, green, and blue types, depending on how they respond to different types of light. Rods are more numerous and light sensitive, but they can't distinguish color. Rods rule your peripheral vision. (6:11)