Gene Fuller wrote:
The definition of irradiance, according to NIST, is power per unit area.
The standard units are W/m2 or lumen/m2.

Exactly how much power can exist in a zero unit of
time?

You previously objected to things that don't match
the real world. Instantaneous irradiance would rely
on an infinitesimally small amount of time, something
that doesn't match reality very well. One would think
you would therefore object to the concept of instantaneous
irradiance since it cannot be measured in reality and
exists only in the math model in the human mind.
--
73, Cecil http://www.w5dxp.com