Cecil Moore wrote:
Every text on EM wave interference that you can find will explain
how the bright interference rings are four times the intensity of
the dark interference rings so the average intensity is two times
the intensity of each equal-magnitude wave.

I certainly misspoke there. The bright interference rings
are four times the intensity of one of the two equal
waves. The dark interference rings are, of course,
zero intensity.

If the intensity of one wave is P, the intensity of the
bright rings will be 4P and the intensity of the dark
rings will be zero. The average intensity will, of course,
be 2P, the sum of the two wave intensities.
--
73, Cecil http://www.w5dxp.com