spectral fluence rate, E λ , o

https://dx.doi.org/10.1351/goldbook.ST07479
Derivative of fluence rate, E o, 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, ν, or wavenumber, ν ˜, and are referred to, when necessary, as in terms of wavelength, or frequency or wavenumber, respectively.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 423