Sentence:  It was possible to make estimates of the quantum yield by observing the extent of <WSD>reduction</WSD> of a uranyl oxalate actinometer solution illuminated for a known time in a typical reaction cell and making appropriate conversions based on the differences in the absorption spectra of uranyl oxalate and of chlorine , and considering the spectral distribution of the light source . 
Meaning of the word marked with <WSD> tags:  any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent