Study protocol for the Melatonin Action Spectrum study performed wih human research volunteers. Participants came in just before midnight (00:00) and had their pupils dilated and then sat in a comfortable office chair with a blindfold on in total darkness until 02:00. They were then exposed to 90 minutes of pure, monochromatic light at one of nine different wavelengths. If it was their control night they stayed blindfolded and were in darkness the entire time (until the end of the experiment at 03:30). Blood samples were taken just before and after light exposure.