Each Petri dish was covered by a polyethylene cling film which absorbed less than 16% of the incident UV light in the wavelength range of 250−350 nm (UV spectrometer, Model U-1900; Hitachi, Japan; www.hitachi-hta.com). While being
stirred continuously (magnetic stirrer), the latex mixture in Petri dishes was irradiated from the top by a bank of six UV lamps (250−350 nm wavelength, 8 W) (Figure 2).