The absolute light outputs of BGO, CsI(Tl) and some new Ce-doped crystals have been measured to an accuracy of about /spl plusmn/5% using calibrated XP2020Q photomultipliers and standard S3590.03 and S2740.03 photodiodes. The use of small crystals, 9 mm in diameter and 1 mm thick, reduces the corrections for imperfections in the light collection process and in the photoelectron collection by the photomultipliers. The measured light-output of 8500/spl plusmn/350 ph/MeV (photons/MeV) for the BGO crystals agree well with the earlier measurement done by Holl et al. (1988). The carried out study highlighted the importances of the spread in the published emission spectra of the crystals which seems to limit measurement accuracy. Finally, a simple comparative method of measuring light output to an accuracy of /spl plusmn/10%, is proposed using an uncalibrated XP2020 photomultiplier and a 1 mm thick BGO crystal as a standard.