Darkness

Darkness is the condition that results from a lack of illumination. It is defined by the absence of visible light. While we often think of it as nothingness, darkness is a complex subject in physics and biology. It affects how we see the world and how our bodies react to the environment.

In many cultures, the term is used metaphorically. It can convey deep feelings of unhappiness or foreboding. Scientists also use the term to describe night. Night occurs specifically when the Sun is more than 18 degrees below the horizon.

Human vision changes significantly when light levels drop. We experience different stages of vision based on luminance. Under normal lighting, we use photopic vision to see clearly. Mesopic vision occurs under intermediate lighting conditions. When light drops below a certain sensitivity threshold, we enter scotopic vision. This is a type of monochrome vision where we can no longer see color. This happens because our cone cells become inactive. Cone cells are the photoreceptors on the retina responsible for color perception. However, they are less sensitive to light than our rod cells.

To survive in low light, vertebrates like humans have evolved specific adaptations. When you enter a dark area, your pupils dilate. This means the black center of your eye grows larger to allow more light to enter. Inside the eye, light-detecting cells also work to adapt. The rods and cones regenerate more unbleached rhodopsin during this process. This helps improve your night vision over time. Interestingly, the perception of darkness is not just the absence of light. The eye is an active organ during perception. If a part of the retina is unstimulated, it can produce a complementary afterimage.

In the field of physics, darkness is described through the behavior of photons. A photon is a particle of light. An object is considered dark if it absorbs these photons. For example, matte black paint appears dark because it does not reflect much visible light. In contrast, white paint appears bright because it reflects much of the light that hits it. An object might even appear dark to us while being bright at a frequency humans cannot perceive. Scientists have even created materials that push the limits of darkness. A company in the United Kingdom called Surrey NanoSystems developed Vantablack. The name combines the acronym for vertically aligned nanotube arrays with the word black. This substance is one of the darkest known, absorbing up to 99.965% of visible light at 663 nm.

Artists have used the concept of darkness for centuries to change how we view art. Painters often use a technique called chiaroscuro to create strong contrasts. They use darkness to emphasize the presence of light in a scene. Shadows are also used to add depth and perspective to a painting. By using darkness as a counterpoint to light, artists create leading lines and voids. These shapes help draw the viewer's eye around the composition. In terms of color theory, mixing primary or secondary colors together can create darkness. This is because each color absorbs certain frequencies of light. In theory, mixing them absorbs all visible light, though in practice, the mixture often takes on a brown tint.

Darkness also holds profound symbolic meaning in global religions and mythologies. In the Judeo-Christian tradition, darkness was present during the first creation narrative. The Book of Genesis describes a void where darkness was over the surface of the deep. In Islam, the Quran mentions both light and darkness as being under Allah's divine will. Light represents guidance and revelation, while darkness can symbolize misguidance or moral corruption. Ancient Greek mythology also personified darkness through the deity Erebus. Erebus was associated with the shadowy realm of death and the underworld. In this view, darkness was an active force representing the unknown and the boundaries of life.

Even in technology and language, darkness has specific definitions. On a standard 24-bit computer display, color is defined by RGB values. These represent red, green, and blue components ranging from 0 to 255. A pixel appears white when all three components are fully illuminated at 255. A pixel appears black when all three components are unilluminated at 0. In linguistics, the history of the word is quite varied. In Old English, there were several different words for darkness, including terms for mist and shadows. The modern word 'dark' eventually evolved from these older roots. Whether in a computer screen or the night sky, darkness remains a fundamental part of our existence.