Footlambert

Footlambert , also foot-lambert ( unit symbol ft.la. or ft.L .; indirectly named after Johann Heinrich Lambert ), was an English unit of measurement for luminance :

${\displaystyle {\begin{alignedat}{4}1\,\mathrm {ft\,la} &={\frac {1}{\pi }}\cdot \mathrm {\frac {cd}{ft^{2}}} \\&={\frac {1}{\pi }}\cdot \mathrm {\frac {cd}{cm^{2}}} \cdot \mathrm {\left({\frac {cm}{ft}}\right)^{2}} &&\approx 1{,}08\cdot 10^{-3}\,\mathrm {la} \;&&&\approx 3{,}426\cdot 10^{-4}\,\mathrm {\frac {cd}{cm^{2}}} \;&&&&=3{,}426\cdot 10^{-4}\,\mathrm {sb} \\&={\frac {1}{\pi }}\cdot \mathrm {\frac {cd}{m^{2}}} \cdot \mathrm {\left({\frac {m}{ft}}\right)^{2}} &&\approx 10{,}8\,\mathrm {asb} &&&\approx 3{,}426\,\mathrm {\frac {cd}{m^{2}}} \;&&&&=3{,}426\,\mathrm {nt} \end{alignedat}}}$

With

• ${\displaystyle \mathrm {cd} }$for the candela
• ${\displaystyle \mathrm {ft} }$for the foot
• ${\displaystyle \mathrm {la} }$for the Lambert
• ${\displaystyle \mathrm {sb} }$for the Stilb
• ${\displaystyle \mathrm {asb} }$for the apostilb
• ${\displaystyle \mathrm {nt} }$for the nit .

literature

• Erna Padel, Hansgeorg Laport: Units and magnitudes of the natural sciences. Fachbuchverlag Leipzig, Leipzig 1967, p. 157.