= Half-plane shadow-boundary intensity
At the geometric shadow boundary of a straight opaque half-plane, the transmitted <Fresnel integral> is exactly half the unobstructed complex amplitude for ideal point illumination. The <Cornu spiral> chord is from its origin to one limiting endpoint, rather than between both limiting endpoints. Therefore $U/U_0=1/2$ and $I/I_0=1/4$. Half the unobstructed intensity would confuse a field fraction with its square. Edge thickness, source extent and alignment can modify the ideal result.
Back to article page
