Chapter 27

Color

Selective Reflection Atoms absorb light at or near their natural

frequencies. Atoms reradiate light at other frequencies

Leaves must absorb everything that is not green

Petals must absorb everything not red.

Different Illumination

What color are the petals of the rose under blue light?Black

What color are the leaves under green light?Green

What is absorbed?

Selective Transmission

Color of a transparent object is the color of the light it transmits.Blue glass appears blue because it absorbs all

other colors.

Radiation Curve of the Sun

0.000.010.020.030.040.050.060.070.08

0 500 1000

Wavelength (nm)

Re

lativ

e E

nerg

y

Simplified Radiation Curve

Wavelength

Real spectral colors

Simplified

Color Addition

CYAN

YELLOW

MAGENTA

These mixtures are the subtractive primary colors

Memorize these!

Yellow Magenta Cyan White

Play mixing the colors yourself

Traditional Color Wheel

Colors equally spaced are said to be primary : Red-Yellow-Blue (RYB) or sometimes Violet-Orange-Green (VOG).

neither RYB nor VOG is equidistant on a perceptually uniform color wheel

RYB cannot mix all colors and we will not consider it further

Complimentary Colors

G + R B + G

B + R

Color Subtraction

White Light

XX Yellow Filter

XX XX Blue Filter

Black

Color Subtraction

Green Dress

Yellow DressXX

Cyan Light

Color Subtraction

Yellow DressXX

Magenta Light

Red Dress