Formulas are derived which enable one to measure relative fluorescence quantum yields of strongly absorbing solutions. Relative fluorescence yield data are presented for quinine in N/10 H2SO4 at four different concentrations, demonstrating that the formulas are correct to within ±3% for sample absorbances ranging from 1.36 to 0.017. The heart of these formulas, an expression giving the fraction of incident light absorbed behind the entrance slit of the emission monochromator, is presented in graphical form.
