The mixing of light is a fascinating scientific phenomenon with principles grounded in physics and human perception. When red and green light mix together, the result is yellow light. Understanding why this occurs requires looking at the physics of light and color.
The Physics of Light and Color
Visible light is part of the electromagnetic spectrum. Light is composed of waves of energy at different wavelengths. The wavelength of light determines its color. Red light has longer wavelengths (around 700nm), while green light has shorter wavelengths (around 500nm).
When red and green light mix, the resulting light has a wavelength between red and green. This wavelength stimulates the cones in our eyes that allow us to perceive the color yellow, at around 570nm. So at a physical level, combining wavelengths of red and green light energy results in yellow light energy.
Additive Color Mixing
The mixing of red and green light is an example of additive color mixing. With additive color mixing, the combination of different colored lights results in a new color light output.
This is different from subtractive color mixing with paints and pigments. When mixing paints, adding more colors together results in darker browns and blacks as pigments absorb certain wavelengths.
But with light, combining different wavelengths just merges them to create a new color. Red and green make yellow because the combination of 700nm and 500nm light equals 570nm light that looks yellow.
Cone Cells and Color Perception
The reason that 570nm wavelength light appears yellow to our eyes is because of the cone photoreceptor cells in our retinas. There are three types of cones cells – red, green, and blue. Red cones are stimulated by long wavelength red light. Green cones respond to medium wavelength green light. Blue cones react to short wavelength blue light.
When the red (700nm) and green (500nm) wavelengths hit our retinas, they stimulate the red and green cone cells at an intermediate level. This stimulation is interpreted by our visual system as the color yellow. The yellow perception arises from both the red and green cones firing together.
Overlapping Emission Spectrums
Another factor in red and green creating yellow has to do with emission spectrums. The emission spectrum of a light source plots its color output across different wavelengths. Looking at the emission spectrums of red and green light shows overlapping regions in the yellow part of the visible spectrum:
| Color | Wavelength Range |
|---|---|
| Red | 620nm – 750nm |
| Green | 495nm – 570nm |
As the emission spectrums of red and green light mix, their overlap in the yellow band combines to produce yellow light output around 570nm.
Color Opponency Theory
An additional idea related to red and green combining to form yellow has to do with color opponency theory. This theory proposes color vision processing through opposing color pairs in our visual system.
According to this theory, there are mechanisms for red vs. green and blue vs. yellow opponency. So red and green are paired against each other, while blue and yellow are complements. This could help explain why mixing red and green appears as the yellow complement.
Factors in Color Mixing
The exact shade of yellow produced by combining red and green light depends on several factors:
- Wavelengths of the red and green light sources
- Relative intensities of the red and green light
- Background color the light is mixed on
Mixing a deep red at 700nm exactly with a middle green around 550nm will produce a bright yellow. The yellow will shift towards orange or lime depending on the red or green dominating. The intensities also affect the brightness of the resulting yellow.
Applications of Red and Green Light Mixing
The principle of red and green light combining to make yellow is applied extensively in technology that relies on mixing colored light. Some examples include:
- Computer monitors – RGB pixels mix varieties of red, green, and blue light to generate all colors.
- Digital projectors – Combining the red, green, and blue components projects a full color image.
- LED lighting – LEDs can emission narrowband red, green, and blue light that mixes to create white light.
In these devices, tuning the relative intensities of the red, green, and blue elements controls the final color output. Red and green mixtures produce yellow hues.
Pigment vs. Light Color Mixing
It’s important to understand light color mixing is different than pigment color mixing. With pigments, combining colors uses subtraction. But mixing colored lights uses addition to make new colors.
For example, mixing red and green paint produces a dark brown. But mixing red and green light makes yellow. This key difference comes from the physics of light vs. matter absorption and emission.
Conclusion
In summary, red and green light combine to make yellow due to the merge of their wavelengths and stimulation of cone cells in the eye. This additive mixing of light colors is based on the physics of light and human color vision. The principles of red and green creating yellow are applied widely in technology to produce colors with light.
