From the spectrum lab Light waves with different

From the spectrum lab: • Light waves with different wavelengths appear as different colors. • Short waves are blue/purple. • Long waves are red.

Missing colors? • Can you find these colors in the spectrum?

More than just wavelength. . . • There is no “brown” or “pink” wavelength of light. • Color is a PERCEPTION, not a reality. That is: –Color only exists in your mind.

False motion

Scintillating Blocks

Shadow and Color

White’s Illusion

Opponent Afterimage

Mc. Collough Effect

Color opponency

What is going on? • You cannot trust your brain. • Your perception of the world is different than the actual world.

Other color craziness • [Greenpro 2009 videos: chameleon, color constancy] • [Himba Tribe study]

Real spectra. . . • Objects emit/reflect light with different sets of wavelengths. –Bright in areas, dark in others:

Perfect emitter at 4000 K:

The Sun:

Electrified neon gas

Spectra and the eye • Eyes can’t see all that detail. • Can’t measure the amount of light of every wavelength. • They check THREE PARTS of the spectrum. . . – red, green, and blue parts

Rods and Cones • Four types of light-detecting cell in your eye: – Rods: very sensitive to all light – Cones: less sensitive, tuned to certain colors (Red, Green, Blue)

Rods and Cones • Sensitivity of the 3 cone cells:

Primary colors • 3 cones → 3 primary colors • Computers and TVs display colors with an “RGB” system for Red, Green, and Blue.

RGB Pixels

Color Addition

Primary colors • “Red, yellow, blue” are a BAD CHOICE for primary colors. • Even in pigments! They can’t make a full color gamut (range). • Cyan, Magenta, and Yellow form the CMYK system for pigment/ink.

Color Subtraction

Different numbers of cones • Some humans only have 2 types of cone! They are color deficient or color blind. (About 1% of men. ) • Some women may have 4 cones!! They’d see differences in color that nobody else does! Tetrachromacy in humans is a new, uncertain discovery.

Colorblindness test

Colorblind simulation: red-green def. blue-yellow def.

Cones in other animals • Most mammals have 2 types. –Dogs don’t see in black & white! –It’s just a limited set of colors. • Higher primates have 3 types. • Some birds, reptiles, and insects have 4 or even 5!

Different cone sensitivity • The cone cells in most birds and insects can detect ultraviolet! • Many things have “hidden” features that they can see!