Time-resolved photoluminescence (PL), at T=8 K, is used to study a graded-width InGaN/GaN quantum well. Across the sample, the well width continuously varies from similar to5.5 to 2.0 nm corresponding to PL peak energies varying between 2.0 and 2.9 eV and to PL decay rates covering four orders of magnitude. The plot of decay times versus PL energies is very well fitted by a calculation of the electron-hole recombination probability versus well width. The only fitting parameter is the electric field in the well, which we find equal to 2.45 +/-0.25 MV/cm, in excellent agreement with experimental Stokes shifts for this type of samples. (C) 2001 American Institute of Physics.