NEW EVALUATION TECHNIQUES FOR SUNSCREENS 58,5 IOO 9o •o 70 6o, 50. 40. 30. 20. •o 300 350 400 WAVELENGT•d mH Figure 2. Ultraviolet transmission and reflection of 0.0254 mm thick film of 7•0 p-amino- benzoic acid in clear viscous solution. Using spectrophotometcr with intcgrating spheres' ---- total transmission, - - -dircct transmission, and ..... percent reflection. Using monochromator: ... direct transmission ß •.. .,-•.- .. _.T-' •" .,... -: ................................ ß ß ! 250 3•0 350 4OO WAVELENGTH rnl• Figure 3. Comparison of two methods for determining transmission on 0.0254 mm thick films of three sunscreen products. Total transmission using spectrophotometer with integrat- ing spheres direct transmission using monochromator. 5% amyl-p-dimethylaminobenzoate q- 10% talc in opaque cream base: ---- total transmission and - - - direct transmission. 10% talc in opaque cream base: ... total transmission and ..... direct transmission. Opaque cream base: ......... total transmission and ........ direct transmission

586 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Studies with Integrating Spheres While the use of the monochromator and photocell indicated that a considerable portion of the light was scattered in a forward direction by samples containing both chemical and physical sunscreens, the total amount of this forward scattered light could not be evaluated due to the geometry of the equipment. Since the phototube subtends an angle of 26 degrees with the sample, only light within 26 degrees normal to the sample was measured. Integrating spheres (Cell Space Reflectance Accessories*) were employed to adapt the Cary Model lzt Spectrophotometer for measure- ment of the total transmission of light (8). In addition to measure- ment of the total quantity of light scattered in a forward direction LIGHT RAYS I PHOTOCELL sAMPLE Figure 4. Direct transmission--speetrophotometer LIGHT RAYS • PHOTOCELL SAMPLE Figure ,q. Direct transmission---spectrophotometer with sample that scatters and transmit light through the specimen, this instrumentation eliminated several errors in measurements due to the monochromator and photocell combination. First, this is a double beam instrument second, its optics were designed fo• exact spectrophotometric measurements third, its readout is auto- matically recorded and fourth, its spectral range permits greater in- formation to be obtained about each specimen. In addition to being able to measure the forward scattered light, the reflected or backward scattered light could also be measured so that the optical properties of each sunscreen were more fully determined. All the thin film specimens of the sunscreen products, used for the monochromator, were also tested by this method. Three measurements were made upon each thin film specimen. The first was the ordinary or * Applied Physics Corp., Monrovia, Calif.