Lumen
Lumen is most commonly used in reference to lighting or illuminance. The lumen is the unit of luminous flux, a measure of the perceived power of visible light emitted by a source, in the International System of Units. The technical definition of a lumen is one candela multiplied by one steradian, a measurement of the amount of light that is contained in a certain area.
Lumen is also used in contemporary computer aided design, in particular 3D modelling and rendering. Lumen is a commonly used render technique, which takes into consideration lighting effects for more realistic renders.
Lumen is also a term used in biology, coming from the is Latin lumen, meaning an opening, which may describe the inside space of a tubular structure, such as an artery or intestine. In the same light lumen is used in material science, in particular it refers to an element in the structure of wood or timber. The lumen is the hollow centre of a cell, where hardwoods may be divided into ring-porous and diffuse-porous trees. In ring-porous trees the vessels laid down at the beginning of the growing season are much larger than subsequent vessels laid down at the end of the season (or ring)
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