Lighting Design Glossary

Light

(Term of photometry)

n. 1. The natural agent that stimulates the sense of sight.
n. 2. Medium or condition of space in which sight is possible.
The Concise Oxford English Dictionary
Fifth Edition, 1964

(noun)
Radiant energy that excites the human visual system. The visible portion of the electromagnetic spectrum extends from about 380 to 770 nm.
Also (colloc.), a source of illumination such as the sun, the sky or an electric lamp.

Light is usually measured in terms of luminous flux. For most purposes other than nuclear physics or astronomy, it can be assumed to travel along straight lines. When it hits a surface boundary, it will either be absorbed, reflected, transmitted or refracted. Reflectance and transmittance can happen directedly (specular) or they can distribute the light throughout the hemisphere above or below that surface (diffuse). Specular reflection (direct transmission) and their diffuse counterparts rarely happen exclusively, but are combined in specific ways with most real life materials.

(adj.)
With a hight reflectance factor; with reference specifically to color, one with a high value.