#light_unit__lightunit  a measure of the visible electromagnetic radiation
  supertype:  #electromagnetic_unit__electromagneticunit__emu  any of various systems of units for measuring electricity and magnetism
  subtype:  #illumination_unit  a measure of illumination
     subtype:  #footcandle  a unit of illuminance on a surface that is everywhere 1 foot from a point source of 1 candle
     subtype:  #lambert__l  a cgs unit of illumination equal to the brightness of a perfectly diffusing surface that emits or reflects one lumen per square centimeter
     subtype:  #lux  a unit of illumination equal to 1 lumen per square meter; 0.0929 foot candle
     subtype:  #phot  a unit of illumination equal to 1 lumen per square centimeter; 10,000 phots equal 1 lux
  subtype:  #luminance_unit__luminanceunit  a measure of luminance
     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
  subtype:  #luminous_flux_unit  a measure of luminous flux per unit area
     subtype:  #lm__lumen  a unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions
  subtype:  #luminous_intensity_unit__candlepower_unit__candlepowerunit  a measure of luminous intensity
     subtype:  #standard_candle__candle__candela__cd  the basic unit of luminous intensity adopted under the System International d'Unites; equal to 1/60 of the luminous intensity per square centimeter of a black body radiating at the temperature of 2,046 degrees Kelvin
     subtype:  #international_candle__internationalcandle  a former international unit of luminous intensity; now replaced by the candela
  subtype:  #exposure.light_unit  the intensity of light falling on a photographic film or plate; "he used the wrong exposure"
     subtype:  #overexposure.exposure  exposure to too much light or for too long a time
     subtype:  #underexposure.exposure  exposure to too little light or for too short a time

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