emissive

Emissive describes something that emits light or other electromagnetic radiation, rather than merely reflecting it. In physics, emission can be thermal, as when a hot object radiates blackbody radiation, or non-thermal, arising from luminescence prompted by electrical, chemical, or optical excitation. The term is used across disciplines to denote self-luminous sources.

Emissivity is a key concept in relation to emissive materials. It is a property of a surface that describes how efficiently it emits radiation compared with a blackbody at the same temperature, with values between 0 and 1. Kirchhoff's law states that at thermal equilibrium, a body's emissivity equals its absorptivity, linking emission to absorption and the spectral distribution of emitted radiation.

In materials science and display technology, emissive materials or surfaces generate light themselves when energized. Examples include LEDs and organic LEDs (OLEDs). Emissive displays produce light directly, as opposed to reflective or transmissive displays that rely on external light sources. In computer graphics, emissive maps encode regions of a surface that emit light, contributing to the scene's illumination without external shading.

In astronomy, emission refers to radiation produced by astronomical objects such as emission nebulae, where gas is ionized by nearby stars and emits characteristic spectral lines. These emissions reveal the chemical composition, temperature, and physical processes occurring within the gas.

Applications of emissive properties span lighting design, energy efficiency, and imaging. Measurements of emissivity and spectral emission inform material selection, coatings, and optical performance across scientific, industrial, and consumer sectors.