- Nocturnal Light Emitting Diode Induced Fluorescence (LEDIF): A new technique to measure the chlorophyll a fluorescence emission spectral distribution of plant canopies in situ(2019-05-09) Jon Atherton; Weiwei Liu; Albert Porcar-Castell; Optics of Photosynthesis Laboratory, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Finland - Jon Atherton; LREIS, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 100101, China - Weiwei Liu; Optics of Photosynthesis Laboratory, Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Finland - Albert Porcar-Castell