What is the "lunar irradiance" received by the Earth from the full Moon? The solar irradiance received by the Earth is 1361 $W/m^2$. What is the lunar irradiance received by Earth from the full Moon in the same units? My first thought was to work it out via apparent magnitude but I don't think that would work out.
You can work in magnitudes, but the magnitude scale is logarithmic.  Instead you can use luminosity.  The moon has a luminosity that is 400,000 times less than the sun, so the maximum theoretical &quot;lunar irradiance&quot; is about 0.0034 watts per square metre.
In practice, the luminosity at the surface is less than this, with Wikipedia quoting &quot;how bright is moonlight&quot; typical values on the Earth's surface of 0.1 lux, equivalent to 0.001 watts of visible light per square metre.