Have you ever wondered what color is? In this first installment of a series on light, Colm Kelleher describes the physics behind colors -- why the colors we see are related to the period of motion and the frequency of waves. See his lesson on color here. By the way, here's a useful dictionary definition for frequency.

Color vision is the ability of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit. Colors can be measured and quantified in various ways; indeed, a human's perception of colors is a subjective process whereby the brain responds to the stimuli that are produced when incoming light reacts with the several types of cone photoreceptors in the eye.

Visible light (commonly referred to simply as light) is electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. Visible light has a wavelength in the range of about 380 nanometres to about 740 nm – between the invisible infrared, with longer wavelengths, and the invisible ultraviolet, with shorter wavelengths.
Artist Neil Harbisson was born completely color blind, but, these days, a device attached to his head turns color into audible frequencies. Instead of seeing a world in grayscale, Harbisson can hear a symphony of color -- and even listen to faces and paintings. See his TED talk here.

Here's a Glossary of Color Science. Color is only one limiting factor of human perception. Once you understand how humans perceive color, research ways that we percieve other things using our eyes.

Colors are of philosophical interest for a number of reasons. One of the most important reasons is that color raises serious metaphysical issues, concerning the nature both of physical reality and of the mind.

Have you ever wondered what it's like to be color blind? Could an increased ability in one of our senses be caused by our lack of ability in another? "No Such Thing As Color" is a nine-minute documentary that shows us what the world looks like through the eyes of Evans Forde, a color blind musician with insightful opinions about the importance of color in our lives.

People love eating pizza, but every style of pie has a different consistency. If "New York-style"--thin, flat, and large--is your texture of choice, then you've probably eaten a slice that was as messy as it was delicious. Colm Kelleher outlines the scientific and mathematical properties that make folding a slice the long way the best alternative...to wearing a bib. See Colm's Lesson on physics here.

The trichromatic theory that is presented in this lesson does not account for all aspects of color perception. For example—if you stare at a red square, then shift your focus to a white background, why do you see a green afterimage? Try this for yourself here. And if you shine a blue light on a yellow banana, the banana will still seem yellow, even though it should appear green. A similar effect can be seen using abstract shapes.

Effects such as these are partially explained by the opponent-process theory and the retinex theory. These theories indicate that the eye and brain carry out some processing that is more complicated than simply detecting the wavelengths of light. The opponent-process theory suggests that there are cells that activate as red under certain conditions, and green under other conditions (the same goes for blue and yellow). The retinex theory suggests that our visual system compares surfaces to their surroundings to help determine what we perceive as color. Like the trichromatic theory, neither of these theories fully accounts for color perception by itself, and the full truth may be a combination or of all three, as well as new theories yet to be formulated. 

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