Despite the best efforts of air traffic controllers, pilots sometimes have to rely on old-fashioned visual sightings to avoid collisions. Although red or white anticollision lights on planes provide a last defense, the field intensity measurements of the lights vary by as much as 30 percent. To provide more accurate intensity measurements of a flash that lasts only a split second, the Federal Aviation Administration has enlisted the National Institute of Standards and Technology to develop a calibration standard. NIST physicists came up with a system that uses two independent calibration methods to produce a primary standard photometer system with an uncertainty of 0.6 percent. The institute is using the system to provide calibrations for reference photometers with the hope of improving uncertainty for field measurements to less than 10 percent.