MidnightSun: software for determining light exposure and phase-shifting schedules during global travel.

The application of circadian principles has the potential to alleviate jet-lag in global travelers, but their application is hampered by the difficulty of determining light exposure along international flight routes. Computerized tools can solve this problem algorithmically. We have developed a program for Macintosh computers, called MidnightSun, which allows researchers to display ambient lighting conditions at any geographical location at any time of the year. The program contains a data base with the latitudes and longitudes of over 3000 airports. It calculates flight paths and durations, and prints a graphical itinerary indicating times of daylight during flights and layovers. Given a travel itinerary and a user-defined phase response curve (PRC) for light, it recommends light exposure times that may accelerate the reentrainment of circadian rhythms to new time zones and reduce the deleterious effects of jet-lag (depending on the efficacy of the PRC and the compliance of the traveler). Other potential applications include determining lighting protocols for photoperiodism experiments and providing data sets for mathematical circadian simulations under naturalistic lighting conditions.