Additive color mixing RGB
Study the mixing of primary colors using one smartphone screen as a source and a second phone's camera as a detector.
Why can a screen that emits only red, green, and blue reproduce all colors? Our eyes have three types of cones sensitive to red, green, and blue, and any perceived color can be produced by the right combination of these three primaries. Using one smartphone as a light source and another as a color detector, you can verify the rules of additive mixing and discover surprising effects when colored objects are illuminated by monochromatic light.
Activity overview:
The student uses two smartphones to explore additive color mixing: one as a colored light source, the other as a color detector.
Level:
Medium and High School
FizziQ
Author:
Duration (minutes) :
25
What students will do :
- Identify the three additive primary colors (red, green, blue)
- Verify the additive mixing rules experimentally
- Measure the RGB components of mixed colors
- Observe how monochromatic lighting changes the appearance of colored objects
- Understand the difference between additive and subtractive color mixing
Scientific concepts:
- Additive color synthesis
- RGB primary colors
- Color perception by the eye
- RGB model
- Complementary colors
- Metamerism
Sensors:
- Camera (RGB color detector)
Material needed:
- Smartphone or tablet with FizziQ
- A second smartphone (colored light source)
- A darkened room
- Colored objects (papers, candies)
Experimental procedure:
Prepare two smartphones: the first as a source (color generator), the second as a detector (colorimeter via FizziQ camera).
On the source phone, display a fully red screen (R=255, G=0, B=0). Set brightness to maximum.
On the detector phone, open FizziQ and select the Camera instrument in RGB color detection mode.
In a dark room, place the source facing the detector (about 5 cm apart). Record the detected RGB values.
Repeat with a green screen (0, 255, 0) then blue (0, 0, 255). Note the RGB values each time.
Test the mixtures: yellow (255, 255, 0), cyan (0, 255, 255), magenta (255, 0, 255). Verify that the detector identifies the correct components.
Display white (255, 255, 255): all three channels should be high and balanced.
Bonus experiment: in the dark, illuminate colored objects (papers, candies) with only the red screen. Observe how their appearance changes.
Repeat with green light then blue light. Photograph the objects under each illumination.
Create a summary table: what color does each object appear under each monochromatic illumination.
Expected results:
The detector correctly identifies the primary colors and their mixtures. Under red light, red objects keep their color while blue and green objects appear black. White objects take on the color of the illumination. The RGB values for mixtures correspond to the additive rules within measurement precision.
Scientific questions:
- Why does mixing red and green light produce yellow, while mixing red and green paint produces brown?
- How does the eye perceive white from three colored lights?
- What is metamerism and why does it matter for color matching?
- Why do colors look different under fluorescent versus incandescent lighting?
- How many colors can a typical screen display?
Scientific explanations:
Additive synthesis creates colors by superimposing lights, in contrast to subtractive synthesis used in paints. The three additive primaries are red, green, and blue.
The fundamental rules are: R + G = yellow, R + B = magenta, G + B = cyan, R + G + B = white. They directly result from how the three types of retinal cones respond to different wavelengths.
A red object does not create light: it reflects red wavelengths and absorbs the rest. Under blue illumination, it appears nearly black because there is no red light to reflect.
Metamerism is the phenomenon where two colors that look identical under one illumination become different under another. It results from objects having different spectral reflectance curves.
The smartphone camera detects colors using a Bayer filter: a grid of R, G, and B micro-filters placed over the image sensor pixels. This mimics the trichromatic vision of the human eye.
Extension activities:
- Why does mixing red and green light produce yellow, while mixing red and green paint produces brown?
- How does the eye perceive white from three colored lights?
- What is metamerism and why does it matter for color matching?
- Why do colors look different under fluorescent versus incandescent lighting?
- How many colors can a typical screen display?
Frequently asked questions:
Q: The screen does not emit perfectly pure red.
R: Normal: screen LEDs have a broadened spectrum. Detected values will be close to (220, 20, 10) rather than (255, 0, 0).
Q: The detector shows unexpected colors.
R: Ensure the room is completely dark. Ambient light adds unwanted color components.
Q: Why does white light from a screen look the same as sunlight?
R: Both stimulate the three cone types equally. However, their spectra are completely different: the screen emits three narrow bands while sunlight is a continuous spectrum.
Q: Can I use this to understand how color printers work?
R: Printers use subtractive mixing (CMYK), which follows different rules. This experiment specifically demonstrates additive mixing.