When we think about color mixing, one of the most common combinations is red and blue. So what color do we get when we mix red and blue light together? The quick answer is that red light plus blue light makes magenta light. However, the full explanation requires delving deeper into the science of light and color. In this article, we’ll explore how combining red and blue wavelengths of light produces the color magenta. We’ll look at the basics of additive and subtractive color mixing, examine the red and blue wavelengths on the visible spectrum, and explain how our eyes and brains perceive the resulting color. With some simple experiments, you can see firsthand how red and blue make magenta.
Additive vs. Subtractive Color Mixing
To understand what happens when red and blue light mix, we first need to distinguish between additive and subtractive color mixing. Both involve combining colors, but in different ways:
Additive color mixing is when different wavelengths of light are added together to produce a new color. This is what happens with light sources like computer/TV screens, theater lighting, and rainbows. With additive mixing, combining more colors results in lighter and brighter colors. Starting with darkness, adding red, green, and blue light together produces white light.
Subtractive color mixing is when pigments, dyes, paints, or inks absorb and reflect different wavelengths of light. Mixing these subtractive colors produces darker colors as more pigmentation is added. Starting with white light, subtractive mixing of cyan, magenta, and yellow pigments produces black.
In our case of mixing red and blue light, we are dealing with additive color mixing. When red and blue wavelengths of visible light are added together, they produce a new color that our eyes perceive as magenta or purplish-pink.
Red and Blue on the Visible Spectrum
To mix colors of light, we need to consider the visible spectrum of electromagnetic radiation. This includes all the wavelengths of light that are visible to the human eye. The visible spectrum runs from about 400 nanometers (violet) to 700 nanometers (red) as depicted here:
| Violet | 400-450 nm |
| Blue | 450-495 nm |
| Green | 495-570 nm |
| Yellow | 570-590 nm |
| Orange | 590-620 nm |
| Red | 620-700 nm |
So where do red and blue fall on this visible spectrum?
Red light occurs in longer wavelengths from around 620-700 nanometers. When we see red, it means a light source is emitting photons mostly in this wavelength range.
Blue light has shorter wavelengths between about 450-495 nanometers. Something that appears blue is emitting more photons in this range.
If we combine light from the long “red” wavelengths and short “blue” wavelengths, our eyes don’t actually have receptors to detect this specific mix. So our visual system perceives the combination as a new color distinct from pure red or pure blue – which we call magenta.
Perceiving Magenta Light
In the human eye, there are three types of color receptors or cones:
– Red cones that detect long wavelengths of light
– Green cones that detect medium wavelengths
– Blue cones detect short wavelengths
When red light (620-700 nm) enters the eye, it activates the red cones but not much of the green or blue cones. This pattern of activation is sent to the brain and interpreted as the color red.
When blue light (450-495 nm) shines into the eye, it stimulates the blue cones more than the green or red cones. The brain perceives this as the color blue.
But when red AND blue light enter together, they stimulate the red and blue cones simultaneously without much green cone activation. Since neither pure red or pure blue caused this activation pattern, the brain essentially invents a new color – magenta – to represent this unique input.
While there is no single wavelength of light corresponding to magenta, having both ends of the visible spectrum present tricks our visual system into seeing it as a distinct color.
Light Mixing Experiments
We can see firsthand how combining red and blue light produces magenta with some simple experiments using flashlights and colored cellophane:
Overlapping flashlight beams: Cover one flashlight with red cellophane and the other with blue. Shine both flashlights onto a wall overlapping the beams. Where the two beams intersect, the light will appear magenta.
Spinning color wheel: Cut a circle out of cardboard and divide it into red and blue colored sections. Attach the wheel to a stick and spin it rapidly. As the wheel spins, the red and blue will merge into a ring of magenta.
Computer screen: On a monitor, display a red square and blue square touching. Where the two overlap, they will mix to display magenta. This works the same way as combining red and blue light.
We can observe the same results by mixing red and blue light sources like colored lamps or stage lighting gels. The key is having both wavelengths enter the eye simultaneously so the red and blue cones are activated together, producing the perception of magenta.
Practical Applications
Understanding how to mix red and blue light allows us to generate magenta in many useful applications:
– TV/computer screens – By adding red and blue light from RGB pixels, displays can show magenta colors. This makes an enormous range of colors possible.
– Printing/painting – Magenta ink is one of the primary subtractive colors in printing alongside cyan and yellow. Combining magenta pigment with red and blue light reflects a magenta color back to our eyes.
– Photography – Red and blue light mixed together can create vibrant magenta hues in photos and digital editing. Photographers may use colored gels or filters to manipulate lighting.
– Theater lighting – Lighting designers often use red and blue gels/LEDs to mix magenta tones on stage for dramatic effect.
– Laser displays – Lasers can project pure wavelengths of red and blue light. Combining beams makes glowing magenta images in 3D displays.
– Fireworks – Certain pyrotechnic compounds emit red or blue light when ignited. Launching these types together results in midair explosions of magenta sparks.
So magenta effects are possible anytime we can precisely control and combine sources of red and blue light.
Conclusion
When red and blue light mix together, the result is a vibrant magenta or purplish-pink color. This additive mixing occurs because red light around 620-700 nm and blue 450-495 nm wavelengths enter the eye simultaneously and activate red and blue color receptors. Since our eyes don’t have receptors for this specific combination, the brain invents a new color perception called magenta. We can observe this red + blue = magenta mixing ourselves using colored flashlights, spinning wheels, computer screens, and more. Understanding the basics of light and color mixing allows us to produce magenta effects in many different applications. So next time you see a magenta color, you’ll know it took the collaboration of red and blue to make it possible!