The Daysimeter: a device for measuring optical radiation as a stimulus for the human circadian system

Optical radiation incident on the human retina stimulates vision as well as provides time-of-day information to the brain's circadian clock. The visual and circadian systems respond very differently to optical radiation. A device, the Daysimeter, was developed and tested to help progress towards a system of circadian dosimetry. The Daysimeter is a lightweight, head-mounted device that records radiation exposure estimates for both the visual and circadian systems, and is specifically designed for field use. In addition to logging spectrally weighted radiation measurements, it records head position and motion to be utilized as a representation of human circadian activity. This paper provides background on the differences between radiation for the visual and circadian systems, as well as a description of the development and testing of this prototype device.