= Angle of incidence
{title2=$\theta_i$}
{wiki=Angle_of_incidence_(optics)}
The <angle of incidence> is the <angle> between the incident <light ray> and the line of the surface <normal vector> at the point of incidence. Use the acute <angle> on the incident side, with $0\leq\theta_i<90^\circ$ for a nongrazing incident <light ray>. An <angle> measured from the surface itself is its complement $90^\circ-\theta_i$. The same convention applies to <wavevectors> in the transparent media with <isotropy> considered here.
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