Additive Color Mixing – Finding Hidden Rainbows

Project Description

Additive color mixing

Young kids have a hard time with additive color mixing because most of their experience is with paint. Paints and pigments follow rules of subtractive color mixing. When kids think about mixing colors, they think that mixing red and green makes a mess. But when you are talking about light, red and green make yellow. They also think that when you mix all the colors, you get black.

With additive color mixing, you literally add, or increase, the wavelengths of light available. So when you combine red, green and blue light, you end up with white!

Download the Worksheet for this Activity

Grades: 1 to 5
Duration: 1/2 Hour – 1 Hour

Supplies: Activity Sheet , Set of 3 LightBLOX, A diffraction grating

NGSS Connections PS4.B: Electromagnetic Radiation
  • Plan and conduct investigations to determine the effect of placing objects made with different materials in the path of a beam of light. (1-PS4-3)
  • Develop and use a model to describe that waves are reflected, absorbed or transmitted through various materials. (MS-PS4-2)
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Light Blox

Light Blox

additive color mixing Additive Color Mixing
Background – Additive Color Mixing

Many students begin with the misconception that the light they experience every day is “clear” and that things create color. In reality, everyday light is composed of many colors, and the colors they see are the result of the interaction between light and matter. The next activity familiarizes students with light and color. It exposes students to the fact that white light is composed of many colors of light. Students will see white light “broken” into a spectrum of colors by a diffraction grating, and they will combine three colors of light (additive color mixing) to make white light. The focus of these activities is on providing materials and guidance to enable exploration and observation. Students record their observations and begin to make sense of their investigations by looking beyond the obvious and forming their own conclusions.

Light can be thought of as either a wave or as a particle. Light is part of a continuous spectrum of “electromagnetic waves,” and the definition of what is “light” varies, but is generally those electromagnetic waves that we can see. Microwaves and radio waves, for example, are light waves that are not detected by the human eye. Each of the wavelengths that are visible to the human eye is defined and experienced by us as a color. Red has the longest wavelength and violet has the shortest wavelength. When waves of light combine with each other, we see a different color! When the three primary colors of light (red, green and blue) are combined, they create white light.

Find Hidden Rainbows

Hold the diffraction grating up to your eye and look through it toward the lights in the room (DO NOT LOOK AT THE SUN). Look to the edge of the slide.

What do you see?

Instructor Tip:
Download the attached PDF for student worksheets and detailed information on the concepts in this lesson.


Step 3

Remove the line caps from all three LightBLOX; turn them on and set them on a piece of plain white paper so that you can see the colors.

Step 4

Move the LightBLOX so that two colors overlap to make a new color.

What colors did you use to make a new color? What new color did you make?

How many new colors can you make? List the colors you used and the new color for each combination. EXAMPLE: RED + GREEN = YELLOW

What happens when you combine all three colors? Can you make “white” light?

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