The absence of color, or black, is a concept that has fascinated humans for millennia. Black is mysterious, elegant, powerful – it evokes a visceral reaction. But what is black on a technical level? What does it mean for a surface to absorb all wavelengths of visible light? In this article, we’ll explore the science behind black, analyzing what gives it its distinctive properties. From physics to physiology, we’ll cover how our eyes and brains perceive black, and why this singular shade holds such symbolic meaning across cultures.
What is Color?
To understand what black is, we first have to understand what color is. Color is a feature of light – it is the way our eyes and brains interpret different wavelengths along the visible light spectrum. This spectrum runs from about 400 nanometers (purples/violets) to 700 nanometers (reds).
| Color | Wavelength (nm) |
|---|---|
| Violet | 380-450 |
| Blue | 450-495 |
| Green | 495-570 |
| Yellow | 570-590 |
| Orange | 590-620 |
| Red | 620-750 |
When light hits an object, some wavelengths are absorbed while others are reflected. The reflected wavelengths determine what color our eyes perceive. For example, a leaf appears green because it reflects mostly green and blue light, while absorbing other wavelengths.
Our brains interpret different wavelengths as distinct colors thanks to special photoreceptor cells called cones. There are three types of cones that are sensitive to short (blue), medium (green), and long (red) wavelengths. By combining and comparing signals from these three cone types, our visual cortex generates the wide array of hues we experience.
So in summary, color is simply the brain’s representation of different wavelengths of visible light. It is a construction of our visual system, not an inherent property of light itself. This will be important to remember as we consider the nature of black.
What is Black?
Black, perhaps surprisingly, is not considered a color by physicists and optical scientists. That’s because black is the absence of visible light. An object that appears black to our eyes is reflecting very little if any light in the visible spectrum. Instead, a “black” surface absorbs nearly all wavelengths of light that hit it.
This means black is actually the absence of perceivable color. Rather than being its own distinct hue, black is what our eyes see when there is no light stimulus to trigger our cone photoreceptors. We perceive it as a color, but technically no light is being reflected to generate a color.
How does an object absorb so much visible light? The pigment or material needs to have special properties. For example, paints and dyes that appear black contain pigments of carbon. The carbon absorbs strongly across the visible spectrum. Inks and paints may also combine cyan, magenta and yellow pigments that together absorb most visible light to produce a rich black. Other chemical compounds can produce a similar effect, absorbing visible light to give surfaces that deep, dark shade.
Perceiving Black
There is something unique about the experience of seeing pure black. Imagine being in a pitch black room, unable to see your own hand in front of your face. Or looking up at a night sky so devoid of light pollution that no stars are visible. These examples illustrate what happens when our visual system lacks the light stimuli needed to activate color-sensing cones.
Relative to our everyday environment, the experience of “true” black is quite rare. Even at night, scattered light from stars and the moon stimulate our vision. When light levels get extremely dim, our eyes adapt by opening the pupil and becoming more sensitive – hence why we can navigate a dark room. Still, most instances of black we encounter in our built environments contain traces of light reflecting or emitting at low levels.
So when we do encounter a total absence of light, it can almost feel like a sensory void or blind spot. Our visual cortex strains to find even the faintest signal, but it finds no light waves to represent as color. While this stimulus void is the reality, our brains often try to fill in or imagine something in these black gaps. This may explain why black can seem to move, shimmer, or take on a grainy texture when stared at in complete darkness. The vision center starts to fabricate its own noise in the absence of real stimuli.
The Physics of Black
From a physics standpoint, perceiving true black requires a surface that absorbs light perfectly across visible wavelengths. Such a surface would reflect back 0% of light hitting it. This is easier said than done, as virtually all natural materials reflect at least some tiny portion of visible light. Scientists are intrigued by the idea of creating artificial materials that could achieve perfect black by completely trapping incoming photons.
Various nanotechnologies and metamaterials show promise for making ultra-black materials. Different techniques include using carbon nanotubes, tiny cavities, or fine nanowire networks to capture light. By controlling structures at the nanoscale, these materials prevent light from bouncing back. The trapped photons either get absorbed or undergo repeat reflections but never escape the surface.
Some examples of current ultra-black materials include:
| Material | Description |
|---|---|
| Vantablack | Made of vertically aligned carbon nanotubes that absorb 99.9% of visible light. |
| Black silicon | Silicon needles with nanoscale pits absorb up to 99.5% of incoming light. |
| Black nickel phosphorous | A nanostructured nickel film absorbing up to 97% of visible light. |
It’s unknown if manufacturing a perfectly black material that absorbs 100% of visible light is possible. But engineers keep striving for new techniques to maximize light absorption. The most black substances today are literally darker than any naturally occurring material. That’s because even the least reflective natural materials, like crude oil, still reflect some light.
Black and Culture
The void-like nature of black gives it cultural symbolism across the world. Black often represents emptiness, darkness, obscurity, or death. But it can also symbolize power, elegance, and seriousness. Here are some examples of black symbolism:
| Culture | Black Symbolism |
|---|---|
| Western | Grief, death, evil, mystery |
| Eastern | Seriousness, authority, sophistication |
| Africa | Spirituality, maturity, fertility of soil |
| Greek/Roman | Darkness, mourning, underworld |
Across cultures, black clothing also carries meaning. In the West, black formalwear represents elegance and prestige. In China, black clothing signals seriousness and authority. Christian priests don black robes as a sign of piety. Brides wear black in parts of India and Bangladesh.
Clearly the perception of black goes far beyond physics and optics. The deeper human fascination with this hue taps into our primeval fears and fascinations with darkness. Because black is experienced so rarely, it retains an elusive, mysterious quality. That mystery gives black much of its cultural power.
Conclusion
What color is the absence of color? Black is not technically a color, but rather the void left when no visible light reaches our eyes. Surfaces appear black by absorbing light across the visible spectrum, leaving none to be reflected back. Yet even though blackness lacks a light stimulus, our visual systems can’t help but project texture, movement, and granularity onto this sensory void. The total darkness of true black sparks our imagination even as it eludes perception. So while black is defined optically as an absence, our experience of it is paradoxically full of cultural meaning.
