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Add and Subtract Colors Guide

Adding and Subtracting Colors Guide

Objectives:

  • Compare and contrast primary and complementary colors of visible light and pigments.
  • Distinguish between mixing colors by addition and by subtraction.
  • Analyze digital images of added and subtracted colors.

STEM Context: A study and analysis of colors of light and pigments can be integrated into topics commonly a part of the K-12 science curriculum that includes:

  • Forms and properties of energy in the electromagnetic spectrum.
  • How the human eye detects visible light.
  • The absorption, reflection, and refraction of visible light.

Examples of Applicable State Standards:

  • Massachusetts Leaning Standard 12 for students in grades 3-5; “Recognize that light travels in a straight line until it strikes an object or travels from one medium to another, and that light can be reflected, refracted, and absorbed.”Source:
  • New York Major Understanding 4.4b for students in Grade 5-8: “Light passes through some materials, sometimes refracting in the process. Materials absorb and reflect light, and may transmit light. To see an object, light from that object, emitted by or reflected from it, must enter the eye.”Source: (Page 27)
  • Pennsylvania Science and Technology Standards 3.4.12 for Grade 12; “Evaluate wave properties of frequency, wavelength and speed as applied to sound and light through different media”Source: (Page 15).

Applicable National Science Education Standards (NAP 1996):

  • Science and Technology Content Standard; Grades 5-8: “Science and technology are reciprocal. Science helps drive technology, as it addresses questions that demand more sophisticated instruments and provides principles for better instrumentation and technique. Technology is essential to science, because it provides instruments and techniques that enable observers of objects and phenomena that re otherwise unobservable….” (Page 166)
  • Science and Technology Standard; Grades 9-12: “Science often advances with the introduction of new technologies. Solving technological problems often results in new scientific knowledge. New Technologies often extend the current level of scientific understanding and introduce new areas of research. (Page 192)

AddingColors of Light Demonstration

Materials

  • A white surface (a screen or white wall) in a very dark room.
  • Red, Green, and Blue spotlightsfrom a hardware store or from scientific suppliers
  • Digital cameras that can upload photographs onto a computer.
  • Computers with access to the internet to ADI software available at the Digital Earth Watch web site ( ) or a STEM DIGITAL version of Analyzing Digital Images software (
  • The DEW and ADI software is accompanies by tutorials about the properties of colors are also included

The Demonstration

Red, green, and blue spotlights can be used to demonstrate how adding two primary colors of light combine to form a complementary color. The three primary colors of light can combine to form white.

  • Students can be provided with a worksheet to record predictions and observations.
  • Students or a teacher can take photographs of selected images on a screen.
  • Shine each primary color separately onto a screen.
  • Shine blue and green light onto a screen to form the complementary color cyan.
  • Shine blue and red onto the screen to form magenta
  • Shine red and green light onto the screen to form yellow.
  • Shine red, green, and blue light onto the screen to form white light.

SubtractingColors of Pigments Hands-on Activity:

Students mix paints or food dyes, take photographs, upload photographs to a computer, and then analyze the photographs.

Materials required include:

  • Cyan, Magenta, and Yellow or Blue, Red, and Yellow paints. Red, Green, and Blue food dye can also be used.
  • Work area to mix pigments, clean-up materials, etc.
  • Digital cameras and Computers with ADI software.

Saving data options when using the line or rectangle tool:

  • Record data directly from the computer display.
  • Use Screen Captures. This method requires an extra step of saving the Screen Capture in a word document but will include average RGB intensities for the area defined by the rectangle tool.
  • Graphs and Histograms can also be saved as JPEG files. Note: JPEG files of Histograms will not include average RGB intensities in an area defined by a rectangle.

An Optional Activity: Use the ADI Line Tool

Draw a line across the photo of the swatches of paint colors.

This feature can be use to detect changes in the intensities of red, green, and blue light along a line across a portion of a photograph

  • Select “Line Tool” in the Spatial Tool Menu
  • Move Cursor to a Starting Point on the Photo
  • Press down using left click to move the line to an end point and release.

Create a graph of colors along a line.

This feature reveals changes in the intensities of red, green, and blue light along a line across a portion of a photograph.

  • Use the File Menu
  • Select “Colors Along Selected Line”.
  • You can turn RGB or the Average Line on and off.

Save the Graph of a Line

  • The graph can be saved as a JPEG file.
  • A Screen Capture can be pasted into a word document.

Examples of Resources

Chapter 28 in the Third Edition of Conceptual Physics written by Paul Hewitt and published by Addison-Wesley has an excellent chapter describing color. The teacher’s edition, the teaching guide, and other ancillaries are particularly helpful.

WGBH Teacher’s Domain has an excellent resource entitled Pigments and Colors.

The University of New Hampshire’s Measuring Vegetative Health web site.