Let us define:

• $d(\lambda_x, \lambda_m)$ = detection efficiency, proportional to solid angle geometry, detector quantum efficiency and optical path trasmission efficiency (comprising both excitation and emission)
• $f(\lambda)$ = distribution density function of emitted fluorescence (spectrum)
• $\phi$ = Quantum yield of the fluorophore
• $I(\lambda_x,\cdot)$ = Intensity of the excitation light

Emitted fluorescence ($F$) from a solution of N fluorescent species can be expressed as a function of excitation (x) and emission (m) wavelengths as follows.