#luminance_unit__luminanceunit  a measure of luminance
  supertype:  #light_unit__lightunit  a measure of the visible electromagnetic radiation
  subtype:  #nit.luminance_unit  a luminance unit equal to 1 candle per square meter measured perpendicular to the rays from the source
  subtype:  #foot-lambert__ft-L  a former luminance unit equal to one lumen per square foot

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