The question of what color red and blue make when mixed together may seem simple on the surface, but it touches on some deep principles of physics and optics. Understanding the interaction of light waves that produce color can unlock insights into the very nature of reality. In this article, we’ll explore the physics behind mixing colors, looking at the behavior of visible light waves and how they interact to form new colors. With some basic knowledge of optics and color theory, we can gain a deeper appreciation for something as fundamental as mixing paints to create new pigments. So let’s dive in and illuminate this colorful intersection of art and science!
The Physics of Color
To understand what happens when we mix red and blue, we first need to consider how we perceive color at all. Visible light consists of electromagnetic waves of different wavelengths, which our eyes detect as various colors. Red light has the longest visible wavelengths, around 700nm, while blue has shorter wavelengths around 450nm. When all wavelengths of visible light strike our eyes at once, we see white light.
But when just a single wavelength dominates, we perceive this as a saturated color. Our eyes have three types of color-sensing cone cells, each most sensitive to either long, medium or short wavelengths. Stimulating the cones differently creates all the color sensations we experience. Mixing light waves is additive, meaning wavelengths combine to form new colors. This is different from mixing pigments like paint, which absorbs certain wavelengths and is subtractive.
Overlapping Waves and New Colors
When red and blue light mix, their waves overlap and interact. Blue light vibrates at around 450 terahertz, while red vibrates at around 430 terahertz. These waves overlap constructively and destructively, producing a new combined wave pattern with crests and troughs. Our eyes don’t detect this new pattern as either red or blue, but rather see it as the distinct color of violet.
Violet light lies between blue and red on the visible spectrum, with wavelengths around 400nm. When you add the wavelengths of blue (450nm) and red (700nm) you get a midpoint of 575nm, landing greenish-blue in the violet range. The exact hue depends on the red/blue ratio. Equal amounts produces a vivid violet halfway between the two. More blue shifts it purple, while more red makes reddish-violet.
Perceiving New Colors
Why don’t we perceive this mix just as a desaturated combination of the two colors, but as a whole new color? This comes down to how our visual system processes signals from the three cone types in our eyes. Red light stimulates the long wavelength cones, while blue excites the short wavelength cones.
Violet strongly stimulates both groups of cones in a new pattern they’re not used to. This unfamiliar ratio of stimulation gets communicated to the brain as a new color distinct from either red or blue. The brain integrates the cone signals into perceiving a color not contained in either one alone. This demonstrates a key principle of color theory known as metamerism – different combinations of wavelengths can produce the same perceived color.
Pigment vs. Light Mixing
Mixing colored lights is fundamentally different from mixing pigments like paint or dye. While light combining is additive, material pigments work by selectively absorbing and reflecting different visible wavelengths. A red paint pigment absorbs blues and greens, reflecting mainly reds. Blue paint absorbs oranges and yellows, reflecting mostly blues.
When you mix red and blue paints, the combined pigment molecules absorb even more wavelengths, reflecting back only violets. This makes the subtractive combination of red and blue paints produce the color purple rather than violet light. The mixing fundamentals are different, even though the resulting colors may appear similar. Making purple paint from red and blue is a subtractive process, removing wavelengths, while violet light is an additive process, overlapping wavelengths constructively.
The CMYK Color Model
This distinction between additive RGB light mixing and subtractive CMYK pigment mixing is important in color theory and graphics. CMYK stands for cyan, magenta, yellow and black, representing the four ink colors used in color printing.
By overlaying these pigments on paper in different amounts, all other colors can be reproduced through absorption/reflection. Mixing 100% cyan and magenta creates blue, mixing cyan and yellow makes green, and combining magenta and yellow produces red. This is the opposite of mixing RGB light colors. The CMYK color model facilitates practical color printing applications, linking color theory to applied technology.
| Color Mix | Light Combination | Pigment Combination |
|---|---|---|
| Red + Blue | Violet | Purple |
| Cyan + Magenta | Blue | Blue |
| Cyan + Yellow | Green | Green |
| Magenta + Yellow | Red | Red |
The Science of Color Mixing
While the specifics vary between mixing light, paint and dye, the underlying principles stem from the physics of electromagnetic waves. When different visible wavelengths combine or interact, they produce new wave patterns our eyes and brains perceive as distinct colors. Isaac Newton demonstrated this with his famous experiments splitting sunlight with a prism into the visual spectrum.
Modern color science builds on Newton’s foundational observations about the nature of light and color. Advances in neuroscience, imaging technology and computing power have deepened our understanding of human color vision and perception. But it all links back to different wavelengths of light and how they combine to make the colorful world we see. Both artists mixing paint and scientists splitting photons rely on the same essential physics of light.
Cultural Context of Color
Beyond the mechanics of mixing, color also has psychological, symbolic and cultural resonance for humans. Red and blue represent fundamental color categories, linked to ancient natural associations like fire and sky. Mixing these primal hues carries symbolic weight, creating offspring colors like purple and violet.
Different cultures also imbue colors with varied meaning. In China, red signifies luck and celebration, while white is the color of death and mourning. In other contexts, red evokes love or danger, while white signifies purity and innocence. Color meaning depends on social constructs, not just physics. But culture draws from a palette generated by underlying wave mechanics.
Applications in Technology
Understanding color mixing contributes to many fields of technology and industry. Displays, cameras and printers all require calibrating mixtures of light or pigments to faithfully reproduce color. RGB and CMYK provide standard models to build upon. Knowledge of how we perceive color also aids compression algorithms to optimize digital image quality. Human vision science informs computer graphics, photography and videography.
Mixing paints for products like cosmetics or dyes relies on mastery over pigment combinations and their optical effects. Materials engineering of quantum dots with tailored light-emitting properties enables new applications in TVs, biomedical imaging and sensing technology. Controlling color at the nanoscale may yield future breakthroughs.
Conclusion
What color does red and blue make? In light, violet. In paint, purple. The answer depends on whether we’re additive mixing wavelengths or subtractive mixing pigments. But in both cases, the physics comes down to how red and blue visible light waves combine and interact. Understanding these foundational principles helps unlock the science behind all color mixing. Whether advanced applications or simple fingerpaints, the vibrant interplay of light underlies the colors we perceive. Mixing paint invokes primal human associations of fire and sky. Mixing light opens windows into the quantum nature of reality.
