lucency

Lucency is the quality or state of being lucent, meaning the ability to emit or transmit light or to be clear and easily understood. The word derives from Latin lucere, “to shine.” In general English, lucency can describe physical brightness as well as conceptual clarity.

In optics and materials science, lucency concerns how much light a material transmits. A transparent substance is highly lucent, a translucent one is partially lucent, and an opaque material is non-lucent. In gemology and mineralogy, lucency is a descriptive measure of light transmission through a crystal or gemstone; it contributes to apparent brightness and color.

In medicine, particularly radiology, lucency is a technical term used to describe regions on an X-ray that permit more X-ray passage and thus appear darker. Radiolucent areas contrast with radiopaque areas, which block X-rays. Lucency is important for interpreting conditions such as air spaces in the lungs, cavities, or lesions where density is reduced.

The term is also used in literature and art to denote perceptible clarity or radiance in imagery or prose, though this usage is less formal than scientific contexts.

See also: lucent, lucidity, transparency, translucency, radiolucent, radiopaque.