Spectral irradiance
= Spectral irradiance
{title2=$E_\lambda,\ E_\nu$}
Incident <radiant flux> per unit area and unit <wavelength> or <frequency>. Integrating $E_\lambda$ over a wavelength interval gives the contribution to <irradiance> in that interval. Conversion between $E_\lambda$ and $E_\nu$ requires the absolute <Jacobian determinant> associated with $\nu=c/\lambda$, as for <spectral radiance>.