diff --git a/src/systems/si/include/units/isq/si/constants.h b/src/systems/si/include/units/isq/si/constants.h
index a0097532..4b3928d0 100644
--- a/src/systems/si/include/units/isq/si/constants.h
+++ b/src/systems/si/include/units/isq/si/constants.h
@@ -26,6 +26,7 @@
 #include <units/isq/si/electric_charge.h>
 #include <units/isq/si/energy.h>
 #include <units/isq/si/frequency.h>
+#include <units/isq/si/luminous_flux.h>
 #include <units/isq/si/power.h>
 #include <units/isq/si/speed.h>
 #include <units/isq/si/thermodynamic_temperature.h>
@@ -53,8 +54,8 @@ inline constexpr auto speed_of_light = speed<metre_per_second, Rep>(299'792'458)
 template<Representation Rep = double>
 inline constexpr auto hyperfine_structure_transition_frequency = frequency<hertz, Rep>(9'192'631'770);
 
-// template<Representation Rep = double>
-// inline constexpr auto luminous_efficacy = 683_q_lm / 1_q_W;
+template<Representation Rep = double>
+inline constexpr auto luminous_efficacy = luminous_flux<lumen, Rep>(683) / power<watt, Rep>(1);
 
 template<Representation Rep = double>
 inline constexpr auto standard_gravity = acceleration<metre_per_second_sq, Rep>(9.80665);