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Where does black fall on the color spectrum? – Utsav, age 17, Navi Mumbai, Maharashtra, India
People love the rainbow of ROYGBIV colors: red, orange, yellow, green, blue, indigo and violet. Human eyes perceive visible light as this array of colors.
You may notice that some colors you can perceive aren’t part of the classic rainbow, though. Where is black, for example?
I’m an associate professor of color science, a field that combines physics and perception. Color scientists are interested in learning more about human vision and applying that knowledge to make color systems – such as in cameras, screens or lighting systems – work better.
To understand where black falls on the color spectrum, first consider what light actually is.
Light is radiation visible to the human eye
Light is energy called electromagnetic radiation. It’s made up of a stream of energy particles called photons.
Each photon has its own energy level. There are two characteristics you can use to describe a photon. Its frequency is how fast it vibrates back and forth – or oscillates – as it travels. And its wavelength is the distance between those oscillations in space.
Light is made up of photons traveling as waves through space.
DrSciComm via Wikimedia Commons, CC BY
As photons with wavelengths within a range of about 400–700 nanometers stream into your eyes, your brain perceives them as light. Scientists call these photons visible radiation. You perceive photons with different wavelengths as different colors.
Photons outside that range of wavelengths are invisible to human eyes. Shorter wavelength energy includes ultraviolet, X-ray and gamma radiation, while longer wavelength energy includes infrared and radio waves.
The human eye can perceive only a small range of wavelengths of radiation.
Ali Damouh/Science Photo Library via Getty Images
Shades and intensities
Color perception is also affected by the quantity of photons – what physicists call the power – at different visible wavelengths. More photons means more powerful light, which looks brighter. A very vivid color consists mostly of photons of similar wavelength. For example, a pure red may consist of photons that all share the same wavelength near 620 nanometers.
A stream of photons with a wider range of wavelengths will appear as a paler, less saturated color. White light, such as natural daylight, consists of photons with wavelengths spread fairly evenly across a wide range of the visible spectrum. LEDs and other electric light sources are not quite as uniform across the spectrum, but they still appear white or achromatic, meaning without color.
Mixtures of wavelengths combine and appear as new colors. The…