Integrating sphere systems can be used to measure the ultraviolet transmittance of sunscreen samples to determine the degree of sun protection offered. Industry standards define various in-vitro solar UV protection metrics for such materials in terms of spectral transmittance over the UV region. The primary metric is described as an “Ultraviolet Protection Factor” (UPF).
For this application, a flash lamp inside an integrating sphere provides diffuse illumination on the sample surface placed at a port in the sphere wall. The sample is shielded from direct illumination by the lamp, and the sphere transfers flux from the lamp to the sample surface by means of multiple diffuse reflections.
A detection system views the sample directionally from outside the sphere, and performs a spectral analysis of the transmitted radiation. The results of this comparison are then used to derive a measurement of the transmittance of the unknown specimen.
Protection factors can be derived from spectral transmittance values by weighting the sample's transmittance curve by a standard solar spectral irradiance irradiance (representing an average amount of radiation provided by the sun at the earth's surface as a function of wavelength) and an erythemal action spectrum (representing the reddening, or sunburn, response of human skin to solar radiation as a function of wavelength).
The area under the weighted transmittance curve represents the degree to which the sample under test transmits harmful solar radiation; the inverse of this value represents the factor by which the sample attenuates such harmful radiation. This inverse, weighted-average UV transmittance is the calculated protection factor SPF.
New in-vitro methods are being embraced by the industry to assess a products UVA protection factor. While UVA radiation does not cause sunburn, it is speculated to cause pre-mature aging of the skin and possibly DNA damage. Most if not all of these new methods require measurement of the products ultraviolet transmittance both prior to and after exposure by a simulated sun to measure the photo-instability of a products active ingredients.
Labsphere offers compact, rugged, easy-to-use instruments for the measurement of UV transmittance, with software specifically tailored to the demands of each of these evolving industry methods.
