The initial intensity of charge recombination luminescence (CRL) emitted by epoxy resins after brief periods of UV irradiation during cure has been measured for a number of resins as a function of cure time. The results are correlated with measurements of extent of reaction of the epoxy groups, using near-IR spectroscopy, and with rheological measurements. They show that the intensity of emission is directly related to the fractional conversion of the epoxy groups, irrespective of the cure temperature, but that the emission only occurs when the conversion is high enough for the resin to be glassy. Attempts to increase the emission by adding aromatic amines failed. It is proposed that, for CRL to be observed, the resin must contain enough OH groups to stabilise the electron traps by solvation and be vitreous enough to prevent immediate recombination of electron-cation pairs.