The instrument uses a photodiode array (PDA) for simultaneousmeasurement of the complete ultra-violet to visible light spec-trum (100–1100 nm) in less than one second. The PDA techniquebrings exceptional reliability and repeatability. The instrument isequipped with a limiting aperture in the instrument which restrictsthe light beam to the central 5 mm of the contact lens.Before conducting each test, the instrument baseline was mea-sured before the transmittance spectra of the CLs were assessed.Each lens was removed from the blister pack using tweezers, wasrinsed with a sterile saline solution (0.9% NaCl) to remove the influ-ence of any surface active agents within the CL solution used instoring the lenses [36]. Similar to the technique used by Harris andco-workers [10], the CLs were then placed directly over the end ofthe aperture of the instrument surface with the concave surfaceplaced perpendicular to the light beam and transmittance mea-surements were obtained at 0.5 nm intervals, from 200 to 700 nm,as this waveband represents the UV–vis waveband within the elec-tromagnetic spectrum.UV–vis spectral transmittance was measured thrice for each ofthe five lenses with the saline solution replaced for each mea-surement. Data from the spectrophotometer were imported intoa personal computer. Using a Microsoft Excel spread sheet (2007),the means of three measurements for each lens were calculatedand used to derive the overall means and standard deviations ofthe measurements for all lenses within a brand.