Description: Light is electromagnetic radiation. In common use, light typically refers to electromagnetic radiation with a wavelength that can be seen with the naked human eye. The wavelength of light that can be seen by humans is broadly in the range of 380–750 nanometers (nm), although most humans have very little sensitivity to light with wavelengths shorter than 400 nm. This is a narrow part of the electromagnetic spectrum that covers a wide range of wavelengths from gamma (the shortest) to radio waves (the longest). More broadly the term light is sometimes applied to any electromagnetic radiation.

The basic properties of light are intensity, direction of propagation, frequency, spectrum, and polarization. Its speed in a vacuum is defined to be exactly 299,792,458 meters per second, and this is one of the fundamental constants of nature. The color of light depends on its wavelength. Violet light has the shortest wavelength in the visible spectrum; red has the longest. Light has multiple sources, natural and artificial; the Sun is the Earth's main source of light. Light is emitted and absorbed in small "packets" called photons that have properties of both waves and particles. This latter phenomenon is called the wave–particle duality.

Related Terms:

• Electromagnetic Radiation
• Visible Spectrum

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".