John Sager Measuring Lettuce Leaf Area, by Hofmeister, Richard K, 1980, Smithsonian Archives - History Div, Agricultural engineer John Sager, a researcher at the Smithsonian's Radiation Biology Laboratory, Rockville, MD, measures lettuce leaf area. Sager has been studying the effects of pulsed, or intermittent, light on plant growth in an effort to determine whether plants grow more efficiently with intermittent radiation or with continuous radiation..