unit:W-PER-M2-SR
$\textit{Watt per steradian per square metre}$ is the SI unit of radiance ($W·sr^{-1}·m^{-2}$), while that of spectral radiance in frequency is the watt per steradian per square metre per hertz ($W·sr^{-1}·m^{-2}·Hz^{-1}$) and that of spectral radiance in wavelength is the watt per steradian per square metre, per metre ($W·sr^{-1}·m^{-3}$), commonly the watt per steradian per square metre per nanometre ($W·sr^{-1}·m^{-2}·nm^{-1}$). It has a dimension of $ML^{-4}T^{-3}$ where $M$ is mass, $L$ is length, and $T$ is time. This unit is the standard SI unit in this category."