Daysimeter (IMAGE) Rensselaer Polytechnic Institute Caption The Daysimeter, shown above, measures an individual’s daily rest and activity patterns, as well as exposure to circadian light -- short --wavelength light, particularly natural light from the blue sky, that stimulates the circadian system. Credit Rensselaer/Dennis Guyon Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.