spectral fluence rate, \(E_{\lambda,\text{o}}\)

https://doi.org/10.1351/goldbook.ST07479
Derivative of fluence rate, Eo, with respect to wavelength, λ. SI unit is W m-3; common unit is W m-2 nm-1.
Note:
All spectral terms may also be defined as derivatives with respect to frequency, \(\nu\), or wavenumber, \(\tilde{\nu}\), and are referred to, when necessary, as in terms of @W06659@, or frequency or wavenumber, respectively.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 423 (https://doi.org/10.1351/pac200779030293)