UVA Star Rating (Boots) 2008 (Revised) Method

An untreated HD2 plate is placed in the Labsphere UV-2000S Transmittance Analyser and used to take a reference blank scan.

Three further HD2 plates are prepared by spreading a small amount of glycerine over the surface (approximately 15µl) using a finger cot. The test material is then applied at a rate of 1.0 mg/cm2 in a series of small dots over the surface of the HD2 plate using a positive displacement pipette and then spread evenly over the surface area (25 cm2) using a naked finger. To ensure an accurate rate of application, the pipette is then weighed without test material and then again with test material. Reference plates to provide a control for the substrate characteristics are produced by applying glycerine only.

Treated test material is then allowed to equilibrate in the dark for fifteen minutes at ambient conditions.

Transmission measurements through test material treated plates are then taken using a Labsphere UV 2000S Ultraviolet Transmittance Analyzer. Each plate is measured at nine locations which will is regulated by a custom template. The test material is then irradiated at a fixed rate of 17.5 J/cm2 using an Atlas Suntest CPS+.

After the irradiation step, all treated test materials is then measured for post-exposure readings using the UV 2000S Transmittance Analyser. The locations shall be as close as possible to the previous sites in order to reduce any variability in measurement due to inhomogeneity of sunscreen distribution across the plate.

The computer system performs all the mathematical calculations necessary to produce the UVA:UVB ratio and star rating. There will be 3 UVA:UVB ratios generated for each test material. A mean of the 3 results is performed and the results are used to categorise the test material according to the Star Rating System.