[en] When using an organic liquid scintillator such as NE213 for neutron spectrometry, the light output as a function of proton energy is needed in order to unfold the neutron spectrum from the scintillator's pulse height distribution. We have measured this function for several detectors over the range 1.5 - 16 MeV approximately, using monoenergetic neutrons from the Harwell 5 MV Van de Graaff accelerator. Results were obtained for a wide variety of sizes and shapes of scintillator cell, and were found to be essentially in agreement within errors. The results were also compared with those of several other workers (amongst whom there is considerable disagreement). Below 10 MeV, there is excellent agreement with one worker and moderate or poor agreement with others; above 10 MeV, agreement is moderate in all cases. We conclude that workers wishing to unfold neutron spectra from NE213 pulse height distributions would be advised to make measurements with their own particular detector configuration, rather than use published functions. (author)