## Light and Illumination

`GSL_CONST_MKS_STILB`
  The luminance of 1 stilb.
`GSL_CONST_MKS_LUMEN`
  The luminous flux of 1 lumen.
`GSL_CONST_MKS_LUX`
  The illuminance of 1 lux.
`GSL_CONST_MKS_PHOT`
  The illuminance of 1 phot.
`GSL_CONST_MKS_FOOTCANDLE`
  The illuminance of 1 footcandle.
`GSL_CONST_MKS_LAMBERT`
  The luminance of 1 lambert.
`GSL_CONST_MKS_FOOTLAMBERT`
  The luminance of 1 footlambert.