Subtractive and additive, and how we see. Pigments - Color by Subtraction Pigments reflect the...
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Transcript of Subtractive and additive, and how we see. Pigments - Color by Subtraction Pigments reflect the...
Subtractive and additive, and how we see
Pigments - Color by Subtraction
Pigments reflect the color you see, and also it’s neighboring color (so green reflects green and yellow and blue)
but Pigments absorb all other colors and turn them into heat.
Primary colors: Red, Yellow, Blue
These shirts are reflecting red light and turning most other colors into heat.
These black clothes absorb all the light that falls on them and reflect no light. All the light is turned into heat.
These white shirts reflect all the colors of light that fall on them, absorbing no colors and turning none of the light into heat
Why does blue pigment + yellow pigment = green light? Yellow absorbs R-B-V, reflects Y-O-G
Blue absorbs R-O-Y, reflects B-G-V
White minus R minus O minus Y minus B minus V = Green
Yellow absorbs violet, red, and blue
light; yellowreflects yellow,
Orange, andGreen light
Blue absorbsYellow and Orange light
Between blue and yellow pigments, all colors are absorbed except for green
Both yellow andBlue pigments reflect Green light
Light - color by Addition
• No pigments involved! Only colored light!
• Primary Colors: Red, Green, Blue
• RR + GG = YELLOWYELLOW
• RR + BB = MAGENTAMAGENTA
• GG + BB = CYANCYAN
• R + B + G = WHITE
Complimentary colors - add two and get WHITE
• GREEN GREEN + MAGENTA MAGENTA = G G + B B + R R = WHITE
• BLUE BLUE + YELLOW YELLOW = B B + G G + R R = WHITE
• RED RED + CYAN CYAN = R R + G G + B B = WHITE
RED PAPER ABSORBS BLUE LIGHT; the reflected light is red
WHITE PAPER REFLECTS ALL COLORS OF LIGHT; the splash looks magenta
MagentaMagenta
What is the color of water?
Water scatters whatever light it gets
Water preferentially absorbs red, turning it to heat and leaving green and blue to scatter back to the eye. That makes shallow water a cyan color. WHITE - RED = CYAN
If the light continues into deeper water, the green is also absorbed, leaving only blue to scatter. WHITE - RED - GREEN = BLUE
Finally, in the deepest water, even the blue is absorbed, leaving nothing to scatter (darkness) WHITE - RED - GREEN - BLUE = BLACK
Why is the sky blue?
Air transmits R-O-Y-G, but scatters blue and violet
The air molecules are about the same size as violet and blue wavelengths (very small). So, instead of traveling straight through, these colors take a “random walk” through the atmosphere; wherever you look, you see blue light coming at you. (Violet too, but we aren’t sensitive to it.)
Why are clouds white?
After all, they are made of water
And the color of water is cyan
Answer: cloud droplets come in all sizes - from violet-light wavelength-sized drops (that scatter violet light) to red-light-wavelength-sized drops. Because all colors of light are scattered, you see all the colors at once coming from the cloud - hence, a white cloud.
Try this at home:
Take a hard, colored candy, like Jolly Rogers
Smash it with a hammer to make all different sized bits
What colors are scattered from the bits?
All of them - that’s why it looks white.
Why is the setting sun red in an orange sky?
Same reason the sky is blue, but . . .
At sunset, the light travels through a layer of atmosphere that is
Thicker and
Full of dust and pollution
So the larger air particles scatter green and even yellow light along with the violet and blue, leaving a red & orange sky and sun.
What color are we most sensitive to?
Hint: it’s the color of fire trucks (new ones) and the signs at the airport and new safety T-shirts
And, we’re most sensitive to it because it’s the color the sun puts out most intensely
What is the green flash?
Green Flash Explained
Sunlight refracts as it goes from the cold air near space through the warm air near the earth’s surface
Which way does it bend?
Blue refracts the most, just as it does in a prism. Red refracts the least.
This means that there is a red sun, and a yellow sun above it, and so forth, ending in a violet sun
Cold Air (dense)
Warm air (rare)
Earth
Cold Air
Warm air
Earth
The shortest wavelength, blue, refracts the most; red refracts the least. The air disperses (separates) the colors of white light.
Cold Air
Warm air
Earth
The image of the sun separates into many images of rainbow colors, one above the other
One flash, two flash, Green flash, blue flash!
What’s with the funny shape?
To understand this, we need to understand mirages . . . .
Mirages are an effect of refraction
When the surface air is hot and the air above is cool, light bends upward
We see the light from a cloud coming at us from the ground
It looks like the sky is on the ground
hot
cold
hot
cold
hot
cold
hot
cold
The same thing happens with the setting sun
But, the light is dispersed into different colors, and
the various images of the sun collide on top of one another
So you get a funny shape with different colors
Green sun
Yellow sun
Orange sun
Red sun
You’ve seen rainbows . . . .
Check out this!