Copyright (c) 2022, (jzeitzer@stanford.edu) rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted with acknowledgment. Description--- These data were obtained by having individuals participate in a series of 16-day studies, each with a 34-hour in-laboratory period. In this between-subjects design, we examined phase shifting in response to variable-intensity (3-9500 photopic lux) flashes at fixed duration (2 ms; n=28 participants) and variable-duration (10 μs-10 s) flashes at fixed intensity (2000 photopic lux; n=31 participants). Acute melatonin suppression, objective alertness, and subjective sleepiness during the flash sequence were also assessed. Description of file in the data repository: 1) The data file is an array of 7 columns and 55 rows. Row 1 is a header row; subsequent rows each represent data from a single participant. 2) Column 1: unique participant ID 3) Column 2: duration of each flash, in seconds 4) Column 3: illuminance of each flash, in lux 5) Column 4: phase change observed after the flash sequence, in hours 6) Column 5: acute change in melatonin concentrations during the flash sequence, in % increase (suppression is negative) 7) Column 6: acute change in sleepiness, as measured by the Stanford Sleepiness Scale, during the flash sequence; this is a Likert-like scale 8) Column 7: acute change in in median reaction time, in milliseconds, during the flash sequence Acute changes were measured before and at the end of the one hour flash sequence.