The combination of blue and green pigments results in the color cyan. When you mix blue and green paints or dyes together, the result is a bluish-green color that we call cyan. But is cyan really the same thing as mixing blue and green light together? In this article, we’ll explore the basics of color theory and find out if combining blue and green wavelengths of light truly makes cyan.
Additive vs Subtractive Color Mixing
There are two main ways that colors can be mixed together – additive and subtractive mixing. Both methods combine colors, but the results can be quite different.
Additive color mixing involves combining different wavelengths of light. In additive mixing, individual light colors are added together to make new colors. This is the method that computer and TV screens use to create colors by emitting red, green, and blue light. When you add red and green light together, the result is yellow. Add green and blue light and you get cyan. Combining red, green, and blue light creates white. The more wavelengths of light you add, the closer the result gets to white.
Subtractive color mixing involves combining pigments. Paints, dyes, inks and other colorants contain pigments that absorb certain wavelengths of light and reflect others. The pigments subtract wavelengths from white light to create color. When you mix blue and green paint, the combined pigments absorb more wavelengths, creating a color that is closer to black. The result is cyan – a dark bluish green. In subtractive mixing, the more pigments you combine, the closer the color gets to black.
So while combining blue and green pigments makes cyan, adding blue and green light does not necessarily make the same cyan color. The difference stems from the fundamentally different ways additive and subtractive colors mix.
Light Wavelengths for Blue, Green, and Cyan
To really understand if combining blue and green light makes cyan, we need to delve into the specific wavelengths of the colors involved.
Visible light from the sun contains all the colors of the rainbow. The wavelengths of visible light range from about 380-750 nanometers (nm). The table below shows the approximate wavelength ranges for common colors:
| Color | Wavelength range (nm) |
|---|---|
| Red | 620-750 |
| Orange | 590-620 |
| Yellow | 570-590 |
| Green | 495-570 |
| Blue | 450-495 |
| Violet | 380-450 |
As you can see, green light ranges from 495-570 nm, while blue ranges from 450-495 nm. There is some overlap between green and blue wavelengths. Cyan light, meanwhile, dominates the wavelengths from 480-510 nm.
So if you combine a 500 nm green wavelength with a 470 nm blue wavelength, the resulting color would fall within the cyan range. Based solely on the wavelength ranges, mixing blue and green could theoretically make cyan. But there are other factors at play.
Chromaticity and the CIE Diagram
While thinking about color wavelengths gives us a good starting point, we need to go a little deeper to truly grasp how blue, green, and cyan relate. This brings us to the concept of chromaticity.
Chromaticity refers to the hue and saturation of a color, independent of brightness. A chromaticity diagram maps out the full gamut of hues and saturations our eyes can perceive. The most widely used chromaticity model is the CIE 1931 xy chromaticity diagram:
The curved edge of the diagram contains all the pure spectral colors from violet to red. Mixing any two colors on the diagram will result in a new color located on the straight line drawn between them.
Looking at the CIE diagram, we see that green and blue wavelengths do not mix directly to make cyan. You can imagine drawing a line between the blue and green points – cyan lies above that line. This shows that combining pure blue and green light would create a color that is desaturated compared to cyan. Cyan has higher purity or saturation than a blue-green mix.
Other Factors Affecting Color Mixing
A couple other factors come into play when combining colored light sources. First, the relative intensities of the lights affect the outcome. If you mix a faint blue light with a bright green, the result will appear more greenish than if you use a strong blue.
Second, most light sources don’t emit pure narrowband wavelengths. Blue and green LEDs have broader wavelength distributions that will change how they mix. LEDs also often have secondary emission peaks that can introduce other hues. These messy real-world factors make it challenging to get a perfect cyan from mixing blue and green LEDs.
Pigment vs Light Mixing
Importantly, the same principles we’ve discussed do not directly apply to mixing pigments. When blending blue and green paints, inks or dyes, the subtractive mixing process combines to make a good cyan. The pigments block overlapping ranges of wavelengths, absorbing more of the spectrum to give a darker, grayer result.
So while blue and green light don’t mix perfectly to make cyan, blue and green pigments do combine to create a nice cyan color. The mixing processes involved are fundamentally different.
Other Ways to Make Cyan
If theoretically combining pure blue and green light doesn’t precisely produce cyan, how can cyan be generated using light? Here are a few other ways:
– Start with white light and filter out all wavelengths except 480-510 nm. This leaves you with pure cyan.
– Use an LED, laser or other light source that directly emits cyan wavelengths without needing to mix colors.
– Combine blue, green, and red LEDs. Carefully tuning the intensities of the three can mix to cyan. More saturation can be achieved than mixing just blue and green.
– Mix highly saturated light from the blue-green boundary of the CIE diagram. The outputs of specialty cyan LEDs approach this region.
So while cyan doesn’t stem directly from mixing blue and green, with the right methods cyan can be crafted out of the visible spectrum. Both additive and subtractive mixing have their means of producing this electric blue-green color.
Conclusion
When it comes to light, blue plus green does not equal cyan. The additive mixing of light waves follows different rules than pigment mixing. Pure blue and green wavelengths combine to make an unsaturated blue-green rather than a vivid cyan. Chromaticity diagrams illustrate that a true cyan requires higher purity than a simple blue-green blend. Factors like the intensities and exact wavelengths of the light sources impact the result. To achieve a strongly saturated cyan through additive mixing requires blending blue, green, and sometimes red sources carefully. In the end, both additive and subtractive systems have the ability to produce cyan, but by differently leveraging the physics of light and pigments.
