The claim that homicellulose contribute to the yellowing of paper has been based on thermal ageing experiments. In experiments designed to test whether the same results would be found after light ageing, hemicellulose fractions isolated from four different pulps. These were applied to filter papers, then aged under fluorescent daylight lamps, black light (UV) lamps and thermally at 90 C and 50% RH. Darkening was intense on heat ageing, negligible under light ageing. Details are given of sample preparation and testing conditions. Similar results were also obtained. Using varying quantities of gamma-cellulose. Black light (UV) lamps and thermally at 90 C and 50% RH.