The mixing of light is a fascinating scientific phenomenon that can be easily observed in everyday life. When green light and red light are combined, the result is yellow light. But why does this happen? The answer lies in the nature of light and the way our eyes perceive color.
How Our Eyes See Color
To understand why combining green and red light makes yellow, we first need to understand a bit about the physics of light and how our eyes see color. Visible light consists of electromagnetic waves of different wavelengths. The wavelength of light determines its color. Red light has the longest visible wavelengths, while violet and blue light have the shortest wavelengths. Green wavelengths are in between.
The human eye has special receptor cells called cones that detect these different wavelengths of light. There are three types of cones:
- S cones respond best to short wavelengths of blue light
- M cones respond best to medium wavelengths of green light
- L cones respond best to long wavelengths of red light
These cone cells send signals to the brain based on how much they are stimulated by the different wavelengths of light. The brain interprets these signals as different colors.
Mixing Wavelengths of Light
When two wavelengths of light enter the eye together, the cones respond to the combined stimulation. The brain then perceives a new color that is some mixture of the two original colors. For example, when red light and green light mix together and stimulate both the L and M cones, the brain sees the result as yellow.
We can visualize this using a simple diagram of the visible spectrum of light:
| Wavelength | Color |
|---|---|
| 700-635 nm | Red |
| 590-560 nm | Yellow |
| 535-490 nm | Green |
Yellow light has wavelengths between red and green. When these wavelengths hit the eye together, the red-sensitive L cones and green-sensitive M cones are stimulated fairly equally, and the brain interprets this as yellow.
Pigments and Filtered Light
Another way to understand red and green combining to make yellow is by looking at pigments and filters. A green filter will block out red wavelengths of light and only allow green to pass through. A red filter does the opposite, blocking green and letting red through. But if you look through a red filter and green filter together, both red and green wavelengths can get through, mixing to be seen as yellow.
This is similar to mixing paint pigments. A red paint pigment will absorb green and blue wavelengths, reflecting back red. Green paint absorbs red and blue, reflecting green. When red and green pigments are mixed, neither wavelength is absorbed. Both red and green light reflect back, combining to be perceived as yellow.
Examples of Red and Green Mixing
We can see the mixing of red and green wavelengths to make yellow in many everyday examples:
- Traffic lights use red, yellow, and green lights. The yellow light is created by combining red and green wavelengths.
- TV and computer screens create color by mixing light from tiny red, green, and blue LEDs (light emitting diodes). Yellow is produced by turning on both the red and green LEDs together.
- The yellow color of sunlight at midday is because sunlight contains both red and green wavelengths of light.
- Plant pigments absorb different colors of light. Chlorophyll in leaves absorbs red and blue, reflecting back green. Carotenoids absorb blue and green, reflecting red and yellow. Together these pigments mix to enable photosynthesis.
The Visible Spectrum
Looking at the full visible spectrum of light also helps show how the mixing of colors produces new hues like yellow:
| Wavelength (nm) | Color |
|---|---|
| 700-635 | Red |
| 590-560 | Yellow |
| 535-490 | Green |
| 450-400 | Violet |
Yellow sits between red and green on the spectrum. Mixing wavelengths from across the spectrum gives us all the colors we see. For example, mixing red light with violet light makes magenta. Mixing blue and green makes cyan. All the possible color combinations arise from the mixing of wavelengths as they stimulate our eye’s color receptors.
Summary
In summary, red light combined with green light appears yellow because:
- Red and green wavelengths stimulate both the red-sensing and green-sensing cone cells in the eye.
- The overlap of wavelengths from red and green light activates the yellow-sensing mechanisms in the brain.
- Pigments and filters combine to allow both red and green wavelengths to be seen together.
- On the visible spectrum, yellow occupies the wavelengths between red and green light.
So while green and red might seem strikingly different to our eyes, they actually combine to create the bright, sunny hue we know as yellow. The mixing of light is responsible for all the magnificent colors we are able to see throughout nature and in manmade objects like traffic signals or TV screens. Science helps explain how this fundamental process works.
