Senior Airman Daniel Hatfield, 28th Civil Engineer Squadron electrical systems technician, changes a phosphorous light fixture at Ellsworth Air Force Base, S.D., Jan. 26, 2016. Phosphorous bulbs are ignited by a ballast, which causes a small spark to light the phosphor in the bulbs to turn on the lights. (U.S. Air Force photo by Airman Sadie Colbert/Released)