Gene Fuller wrote:
Does Hecht really say that more power goes into the glass than enters
the 1/4WL film? Can we somehow bottle this free energy and save the world?

Gene, here's a complete fixed font irradiance diagram of
the air to thin-film interface including all components.
Reflectance = 0.01, Transmittance = 0.99

Forward irradiance component

Ifor=1W --|
|-- I1=0.99W
I3=0.01W--|

air | thin-film

Reflected irradiance component

|-- Iref=0.0101W
I4=0.01W--|
|-- I2=0.0001W

I1 + I2 + 2*SQRT(I1*I2) = 1.0101W = Ifor in the thin-film
This is "total constructive interference" per Hecht.

I3 + I4 - 2*SQRT(I3*I4) = 0W = Iref in the air
This is "total destructive interference" per Hecht.

Those are the irradiance equations from "Optics", by Hecht.
As Hecht asserts, the destructive interference equals the
constructive interference and the reflections toward the
source are canceled.
--
73, Cecil, http://www.qsl.net/w5dxp