Outdoor tests take too long, often stretching for several years. Indoor devices can accelerate the testing process but do not always provide optimal results. Researchers at the National Institute of Standards and Technology have developed a spherical device that distributes UV radiation uniformly into 32 external specimen chambers, ensuring repeatability and reproducibility of test results. The device is calculated to accelerate UV exposure 30 to 65 times faster than natural solar exposure. Sealed quartz tube bulbs are arranged uniformly around an opening at the top.
Microwave energy heats the gases inside the bulbs to form a high-temperature plasma.
The plasma radiates up to 1800 watts of ultraviolet light into the sphere and back out into its specimen chambers. Materials exposed to the sphere's UV light for one day potentially receive the equivalent of 65 days of sun. Two months could equal more than 10 years of solar exposure. The sphere's design allows researchers to test different samples of the same material under precisely the same UV light conditions in separate specimen chambers, each of which can be set for different temperatures, humidities and physical stresses. NIST researchers used highly penetrating neutron radiation to probe the interatomic distances in several prototype springs.