If we sum a large number of dipoles which oscillate in a random phase, then the power output scales linearly. This is because
σ^2(X + Y) = σ^2(X) + σ^2(Y),
where X and Y are independent random variables and σ^2 denotes the variance. The energy density of an electromagnetic wave is ~ E^2, where E is the electric field. The expectation value of E is zero. The variance tells the energy density.
The equation above explains why energy is conserved in the interference of random dipoles. Constructive and destructive interference balance each other.
In the previous posting we looked at scattering of a photon from a block of glass. In that case, we can get an almost total destructive interference of scattered waves if we let the refractive index to be 1 at the surface and gradually increase it inside the glass block.
Conclusion: there is no general rule how much destructive interference of output waves there is for a system of oscillating dipoles. We have to determine it for each case individually.
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