Keith Dysart wrote:
I take this to mean that with largely incoherent sources
the intensity is doubled everywhere.

Being a little more precise:
With mutually incoherent equal-magnitude sources,
the maximum possible peak intensity is double the
intensity of a single wave. There's no interference.

For "largely incoherent sources", the peak intensity
would be slightly more than double.

With largely coherent sources, the average intensity is
doubled everywhere, but there is also a spatial distribution
where the peak intensity is 4 times, but the minimum is zero
(thus the same average of two).

With mutually coherent equal-magnitude sources,
the maximum possible peak intensity is four times
the intensity of a single wave, i.e. there is total
constructive interference. (This can happen
at a Z0-match in an RF transmission line.)

For "largely coherent sources" the peak intensity
would be slightly less than four times.
--
73, Cecil http://www.w5dxp.com