radiant power, P

https://dx.doi.org/10.1351/goldbook.R05046
Power emitted, transferred or received as radiation. SI unit is J s −1 = W.
Notes:
  1. Mathematical definition: P = d Q / d t. If the radiant energy Q is constant over the time interval, P = Q / t.
  2. In radiometry, flux (Φ) is used with the same units as P. The symbol Φ is reserved for quantum yield in photochemistry. Therefore, the use of flux (Φ) is not recommended.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 410