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Additive color

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There are 2 ways to create color:

additive model/RGB:

Make new colors by adding beams of light

RGB: red, green, blue

subtractive model/CMYK:

Making new colors by adding pigments (dyes, inks, paints)

CMYK: Cyan, Magenta, Yellow, Black

This lesson is on the additive color model.

Additive and Subtractive primary colors

This lesson is from Apple Valley High School
http://www.district196.org/avhs/dept/science/physics/physicsweb04/AVHSPhysics/color-notes.html

Additive color: mixing beams of colored light

We start with no light, and add colors of light together to get the final result.

Complementary colors: These are two colors (one primary, one secondary) which, when added together, make white light. They are:

magenta and green
yellow and blue
cyan and red

Three projectors emit the 3 primary colors of light (red, green, blue) on a “white” screen.

Where two of the primary colors overlap you’ll find a secondary color.

Where all three overlap you’ll find white light.

Complementary colors are always across the white spot from each other in this “color wheel”.

light-boxes-make-white-light

Mixing colors of light

We have a white screen. It can reflect any color of light we shine on it.

Now shine red light on the surface – and hold up a hand so we cast a shadow.

The shadow will have no light hitting it so it will be black, while the rest of the screen would reflect the red light.

red-light-on-hand-hewitt

Now let’s add a green light on the right side of the picture.
Check out what happens now!

red-and-green-light-on-paper

Notice how the screen has both green and red which makes yellow.

The shadow on the left blocks the green light, so the red light is the only light that hits that particular shadow.

The right shadow is green for the same reason. Cool, huh?

Now let’s add blue in the center. Check it out!

red-blue-and-green-bulbs-on-paper

The screen has gone to white since it has red, green and blue striking it’s surface.

It reflects all 3 colors back to our eyes, so we see white.

The shadows are now the secondary colors (magenta, yellow, cyan).

This is because each shadow has 2 of the 3 primary colors hitting it, so it becomes one of the secondary colors.

Note: All of this is ONLY for mixing rays of light.
If you try mixing pigments (the colored chemicals in paints, crayons, dyes, markers, etc) we will get totally different results.

Looking at a white object in a white light

White objects in white light

.

White object in blue light

m

white object in red light

m

red object in red light

m

red object in blue light

m

red apple and green pear in white light

m

red apple and green pear in red light

m

red apple and green pear in blue light

 

Problems

When three colored lamps, red, blue and green, illuminate a physics instructor in front of a white screen in a dark room, three slightly overlapping shadows appear. Specify the colors in regions 1 through 6.

three-color-lamps-on-a-guys-face-additive-color

http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_NextTime_Shadows2.xml

External lessons

PhET lab color vision

Additive and Subtractive Color in early color movies

http://www.widescreenmuseum.com/oldcolor/oldcolor.htm

Learning Standards

SAT subject test in Physics: Waves and optics
• Physical optics, such as single-slit diffraction, double-slit interference, polarization, and color.

Massachusetts Arts Curriculum Framework: The Practice Of Creating
PreK- 4 Visual Arts Standards – Identify primary and secondary colors; predict and demonstrate the effects of blending or overlapping primary colors; demonstrate knowledge of making dark to light values of colors. Identify and use basic two-dimensional hollow and solid geometric shapes (circle, triangle, square, rectangle) and three-dimensional forms (sphere, pyramid, cube).

Grades 5-8 Visual Arts Standards – Create compositions that reflect knowledge of the elements and principles of art, i.e., line, color, form, texture; balance, repetition, rhythm, scale, and proportion. Demonstrate the ability to apply elements and principles of art to graphic, textile, product, and architectural design.

Massachusetts Arts Curriculum Framework
The Arts Disciplines: Visual Arts
PreK–12 STANDARD 2: Elements and Principles of Design

By the end of Grade 4: 2.1 Students will, for color, explore and experiment with the use of color in dry and wet media Identify primary and secondary colors and gradations of black, white and gray in the environment and artwork.
By the end of Grade 8: 2.7 Students will, for color, use and be able to identify hues, values, intermediate shades, tints, tones, complementary, analogous, and monochromatic colors. Demonstrate awareness of color by painting objective studies from life and freeform
abstractions that employ relative properties of color

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