Jim Kelley wrote:
Not exactly as per Hecht. Note to the casual reader: please be advised
that unlike Cecil, Eugene Hecht does not claim that power is equal to
irradiance.

Here's a quote from "Optics", by Hecht concerning irradiance.
"... since the *power* cannot be measured instantaneously, the
detector must integrate the energy flux over some finite time,
T. ... The time-averaged value of the Poynting vector, ..., is
a measure of I." - where I is the irradiance and the Poynting
vector is the power flow vector.

Hecht seems to treat irradiance the same way that RF engineers
treat power flow vectors. Hecht also says that integrating energy
flux over some finite time is a measure of power. Presumably,
that could be a non-destructive mental integration.

In "Optics", the definition of irradiance is: "the average energy
per unit area per unit time". That's the same definition as the
power flow vector from the IEEE Dictionary: "... *power* per
unit-area propagating in the wave".

Also from the IEEE Dictionary: "Poynting vector - ... The integral
of P(t,r) over a surface is the instantaneous electromagnetic
*power flow* through the surface."

Do you really think Hecht used the Poynting vector while ignorant
of its definition?

When an astronomer draws a spherical boundary around the sun and
calculates the power output of the sun, most of that power is
heading out to empty space and doing no work. Maybe you should
campaign to have that calculation removed from publication.
--
73, Cecil http://www.w5dxp.com