wavelength, wavenumber or frequency at which the total intensity of emission of light by a sample does not change during a chemical reaction or physical change. The terms isolampsic and isostilbic are sometimes used.
Note:
This term may be misleading because it does not specifically refer to light emission.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 358 (https://doi.org/10.1351/pac200779030293)