A unit of luminance (photometric brightness) equal to 1/pi candela per square foot, or to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot, or to the average luminance of any surface emitting or reflecting light at that rate
A unit of luminance equal to 0 3183010 candela per square foot, or to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at a rate of one lumen per square foot, or to the average luminance of a surface emitting or reflecting light at that rate An unobstructed sky of one footlambert uniform luminance contributes one footcandle of illuminance on a horizontal plane