= Power-law spectral K correction
{title2=$S_{\nu_o}=P_{\nu_o}(1+z)^{1-\alpha}/d_L^2$}
For emitted spectral power per steradian $P_\nu\propto\nu^{-\alpha}$, the <luminosity distance> gives $S_{\nu_o}=(1+z)P_{(1+z)\nu_o}/d_L^2$. Photon energy and arrival-rate redshifts supply two factors of $1+z$, while the observed frequency interval is reduced by one. Substitution of the power-law spectrum gives the displayed <K correction>. This convention uses spectral flux per unit frequency and power per steradian; using per unit wavelength or total spectral luminosity changes the corresponding factors.
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