W/m2 Lux Conversion

The standard for measurement of solar irradiance utilizes the units of watts per meter squared (W/m2).  Irradiance meters are both costly and limited in the ability to measure low irradiance values.  With a lower cost and higher sensitivity in low light conditions, light meters measure illuminance utilizing the unit of Lux.  A conversion factor would enable the use of light meters to evaluate PV performance under low solar irradiance conditions.  This conversion is a supplement to Luminous Efficacy that compares atmospheric light in units of lumens to solar irradiance in un