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What does blue plus green light equal?

What does blue plus green light equal?

The combination of blue and green light is a fascinating topic in the field of optics and color perception. When different wavelengths of visible light mix together, the result can be surprising and complex. In this article, we will explore the basics of combining blue and green light, look at the implications for human color vision, and see what interesting effects can occur when these two colors are brought together. Understanding light mixing and the perception of color requires diving into some physics and neuroscience, but the phenomenology of blue, green, and blue-green combinations is accessible to anyone with curiosity to spare. Let’s mix some metaphorical pigments and see what new shades we can create!

The Physics of Blue and Green Light

To understand what happens when blue and green light mix, we first need to understand what makes blue and green light distinct from one another. Visible light can be described in terms of wavelengths within the electromagnetic spectrum. Blue light has a relatively short wavelength, ranging from about 450-495 nanometers (nm). Green light has a longer wavelength, ranging from 495-570 nm. The wavelengths are one indication that these two colors deliver different amounts of energy – blue photons pack a stronger energetic punch than green photons.

When two wavelengths of light overlap, the result is a combined waveform with a new wavelength. In some cases, this produces an entirely new color. For example, red light around 700 nm combined with blue light near 450 nm gives a summed wavelength corresponding to cyan light around 550 nm. Other color combinations like yellow and blue can sum to produce white light.

So what happens when you add blue and green light? Because their wavelengths are fairly close together in the spectrum, the result remains perceptibly greenish or bluish, depending on the relative intensities. Mixing equal intensities gives a wavelength around the middle of the blue-green range, around 500 nm. This yields a pastel cyan sort of color. However, changing the proportions shifts the sum toward either the blue or green side.

Color Perception and the Blue-Green Balance

The way humans perceive color also influences what happens when blue and green light mix. Our color vision depends on three types of cone cells in the retina that are most sensitive to red, green, and blue wavelengths. The response of these cones to a given wavelength determines how the brain interprets the color. Mixing blue and green light stimulates both the blue-sensitive and green-sensitive cones. If the intensities are nearly equal, neither cone dominates, and a balance between blue and green is perceived.

Imbalances in the blue-green color mix can have perceptual effects. For example, having more blue than green will be perceived as a bluish cyan. But at extreme imbalances, the color may be categorized differently. A strong blue signal with little green may be seen as simply “blue.” A strong green signal may fully override the blue and also be seen as just “green.” Our color perception categorizes the mix based on the most strongly activated cone type.

This means you can mix blue and green light but still have the mix be perceived as blue or as green under the right intensity conditions. The balance point where cyan or teal is perceived requires just the right proportions.

Interesting Blue-Green Mixing Effects

Beyond simply making cyan hues, mixing blue and green light can produce some surprising effects due to the interactions between wavelengths and human perception:

– **Critical flicker fusion:** Mixing blue and green at certain modulation rates can produce interesting stroboscopic effects. Our eyes can fuse rapid pulses into steady colors up to about 60 pulses per second. Mixing blue and green pulses above this critical flicker fusion threshold produces various flickering effects.

– **Depth effects:** Using crossed polarizer filters and polarized blue-green light can create vivid illusions of depth and 3D structures. These effects exploit how polarization affects the mixing and transmission of light.

– **Binocular luster:** Presenting slightly offset mixtures of blue and green light to each eye can create lustrous, shimmery surfaces. This binocular luster points to neural processing happening beyond just what each eye’s cones detect.

– **Blue-green afterimages:** Staring at blue-green mixtures can lead to vivid negative afterimages as the cone cells become fatigued. Complementary reddish hues often appear when looking at blank fields after viewing bright cyan stimuli.

– **Simultaneous contrast:** Surrounding colors strongly influence how blue-green mixtures are perceived. Identical cyan patches can appear greenish or bluish depending on red or yellow contexts. This demonstrates the complex spatial interactions that occur in color vision.

Mixing Pigments vs. Mixing Light

An interesting distinction arises when we compare mixing blue and green light versus mixing blue and green pigments. With lights, the wavelengths add to produce new spectral combinations. But with pigments, mixing involves the physics of reflectance and filtering.

For example, mixing blue and green paint does not produce a cyan paint that reflects cyan light to the eye. Instead, it makes a dark muddy or grayish color. This results from each pigment filtering out some wavelengths, leaving less total reflection. Mixing blue and green pigments produces a brownish-green mix without any cyan hues.

So mixing blue and green light is very different than mixing blue and green pigments. Be sure not to confuse additive color mixing with subtractive color mixing!

Examples of Blue and Green Light Mixing

Here are some examples of blue and green light mixing in the real world:

Where Blue and Green Mix Effects and Applications
Cyan laser light Mixing blue and green lasers or LEDs produces a vivid cyan beam for displays
Water absorption Water selectively absorbs longer red/orange wavelengths, leaving scattered blue/green light
TV and computer screens Blue and green pixels mix to produce other colors including cyan
Cyanobacteria bioluminescence Some species of bioluminescent bacteria emit blue and green light
Cyan fireworks Special compounds can emit blue/green hues when ignited
Dichroic filters Optical coatings can selectively reflect/transmit blue and green
Cyan LED light bulbs White LED bulbs mix blue and green (and red) LEDs

Wherever you have blue light and green light combined, whether in nature, technology, or displays, you get the potential for interesting and beautiful cyan effects.


When blue light and green light mix, the result is a distinct bluish-green cyan color. The specifics depend on the relative intensities and how our eyes perceive the combined wavelengths. Mixing blue and green can produce intriguing optical phenomena and illumination. It all stems from the fundamentals of light physics and color vision.

So next time you encounter a cyan blue-green color in the world, think about the hidden blend of wavelengths and visual processing giving rise to that hue. Blue plus green equals cyan, but not always in the ways you might expect! Our sensation of color depends on complex pathways from photons to perception. Exploring the interactions of different wavelengths gives insight into both physics and neuroscience. Mixing up some blue and green is a great way to illuminate how light and color work.