Summary:

Red cellophane (like that in the color filters) transmits only red light, so when light hits the filter, only red light emerges. A yellow filter transmits both red and green light, blocking (subtracting) the blue light. The colors transmitted by each primary and secondary color filter are summarized in Figure 21.

Yellow, cyan, and magenta are called the primary subtractive colors because each subtracts one primary color of light. By using more than one filter (stacked, so that the light passes through both filters before being projected), you can subtract more than one color. For example, shining light through yellow and magenta filters subtracts blue and green, leaving red. Red light will be projected.

Learning Goals / Objectives:

To learn the primary subtractive colors and how they subtract.

Background

Anticipatory Set:

How do the primary subtractive colors combine?

Instructions / Activities:

• Plug the light box into the power supply. For this experiment, you will use the end of the light box without the swinging doors.

                                                   

• Support your index card (or other screen) so that the colors can be projected onto it.
• Place the yellow filter in the slot.
• What color is projected onto the screen? _______
• What primary colors make up this color of light? and _______
• What primary color is subtracted by this filter (what color is missing from the projected light)? _____
• Remove the yellow filter and place the magenta filter in the slot.
• What color is projected onto the screen? _______
• What primary colors make up this color of light? and _______
• What primary color is subtracted by this filter (what color is missing from the projected light)? _____
• Remove the magenta filter and place the cyan filter in the slot.
• What color is projected onto the screen?
• What primary colors make up this color of light? and _______
• What primary color is subtracted by this filter (what color is missing ,from the projected light)? _____
• Put yellow AND cyan filters in the two slots, so that the light passes through both filters.
• What color is the projected light? ____ _
• Explain the color you see, based on the subtractive properties of the filters.
• Put yellow AND magenta filters in the two slots, so that the light passes through both filters.
• What color is the projected light? _ _ _ _
• Explain the color you see, based on the subtractive properties of the filters.
• Put cyan AND magenta filters in the two slots, so that the light passes through both filters.
• What color is the projected light?
• Explain the color you see, based on the subtractive properties of the filters.
• Put cyan, magenta, and yellow filters in the slots, so that the light passes through all three.
• Describe the light that is projected now.
• Explain what you see, based on the subtractive properties of the filters.

Assessment:

Teachers Discretion

Wrap-up / Closure:

• The three primary subtractive colors are _ _ _______ ____ . They are called primary subtractive colors because each subtracts one of the ______ ___ colors of light.
• Complete each of the following light subtractions:
• White – Blue ->
• White – Green ->
• White- Red->
• White – Blue – Green ->
• White – Blue – Red ->
• White – Red – Green ->
• White – Red – Green – Blue ->
• What primary subtractive color filters could you use to demonstrate each subtraction described above? List one, two, or three filters for each.

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