= Destructive interference intensity
{title2=$I_{\min}=(\sqrt{I_1}-\sqrt{I_2})^2$}
For the same mutually coherent, equally polarized <monochromatic waves>, the <wave interference> minimum occurs at <phase difference> $\delta=(2m+1)\pi$, with <integer> $m$. The <wave amplitudes> subtract, giving $I_{\min}=I_1+I_2-2\sqrt{I_1I_2}$. Complete cancellation requires equal individual <wave intensities>; $1$ and $0.25$ leave $0.25$ in their common unit. A dark band is a local minimum, and the average across an <interference fringe spacing> still obeys <conservation of energy>.
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