There are 2 main definitions of lumen in English:


Syllabification: lu·men
Pronunciation: /ˈlo͞omən
(abbreviation: lm)


The SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.
More example sentences
  • This 18-volt light offers 500 lumens of searing white light for 20 minutes, or you can employ the 250-lumen lamp assembly to extend run time to one hour.
  • It produces 25 lumens of white light without the distracting ‘black holes’ emitted by many flashlights.
  • In almost every case the electronic ballast ensures the highest mean lumens per watt, both by inherent efficiency and, in the case of metal halide lamps, by better lamp power management.


late 19th century: from Latin, literally 'light'.

Definition of lumen in:

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There are 2 main definitions of lumen in English:


Syllabification: lu·men
Pronunciation: /

noun (plural lumina /-mənə/)

The central cavity of a tubular or other hollow structure in an organism or cell.
More example sentences
  • Clear cell carcinoma may contain more ‘condensed’ nonclear cells with pink cytoplasm, mimicking ducts, albeit lacking lumina.
  • These cells were found minimally invading the liver, by direct extension, but were readily found within the lumina of blood vessels and lymphatics.
  • Histologically, the disease is characterized by a bizarre population of neoplastic cells that are found systemically within the vascular lumina.


late 19th century: from Latin, literally 'opening'.



More example sentences
  • Unlike an infection, endometriosis does not damage the luminal epithelium of the Fallopian tube and thus surgery is more likely to be successful.
  • Unfortunately, the absence of endothelial cells at the luminal surface of prosthetic vascular grafts potentiates thrombosis and neointimal hyperplasia.
  • The upper airway size is determined by the balance between static pharyngeal mechanics, neuromuscular activity, and luminal pressure.

Definition of lumen in: