Photometric passband
= Photometric passband
A photometric passband is the wavelength-dependent response used for a brightness measurement. An energy-weighted measurement is $I=\int\eta_\lambda F_\lambda\,d\lambda$, with <spectral flux density> $F_\lambda$. Photon-counting conventions can instead include a factor $\lambda/(hc)$; the calibration must use the same convention as the measurement.