To assess the degree of CL observed in EBEC MicroED patterns, we initially recorded diffraction from 6 salen crystals at increasing values of incident electron beam flux on the crystal: ~0.01, 0.03, and 0.045 e -/Å 2 /s (Supplementary Figure ). We chose salen ligand crystals since their unit cell, morphology and degree of order were characteristic of the type of organic small molecule microcrystals that might yield ab initio structures by MicroED. We recorded one second-long, 60-frame movies under these conditions, noting that the illuminated crystals were stable and did not suffer any radiationinduced decay in diffraction signal during that exposure. Electron count distributions from all measured reflections detected in second-long movies from various crystals showed maximum counts ranging from 71 to 206 e -/pix/s for an incident flux of 0.01 e -/Å 2 /s, and maximum counts ranging from 8 to 246 e - /pix/s for the highest incident flux of 0.045 e -/Å 2 /s (Supplementary Figure , Supplementary Table ).