Sentence:  It was possible to make estimates of the quantum yield by observing the extent of reduction 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 <WSD>absorption</WSD> spectra of uranyl oxalate and of chlorine , and considering the spectral distribution of the light source . 
Meaning of the word marked with <WSD> tags:  the spectrum of electromagnetic radiation that has passed through a medium that absorbed radiation of certain wavelengths