described in subsequent sections. Quantity Unit Name Symbol watts [lumens] Radiant flux [Luminous flux] W [lm] Radiant energy [Quantity of light] joules [lumen sec.] J [lm·s] Irradiance [Illuminance] watts per square meter [lux] W/m [lx] Radiant emittance watts per square meter W/m [lm/m ] 2 [Luminous emittance
