spectral radiant energy, Qλ 

https://doi.org/10.1351/goldbook.ST07480
Derivative of radiant energy, Q, with respect to wavelength λ. SI unit is J m1; common unit is J nm1.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 425 [Terms] [Paper]