The ui.R and server.R files make this PPFD by time Shiny app that calculates the expected PPFD (photosynthetic photon flux density in units of µmol m-2 s-1) at a user selected time of day, day of the year, and latitude and longitude. The expected DLI (daily light integral, in units of mol m-2 d-1) for that location on that day is also calculated.
More information about these calculations is given in the FAO Crop evapotranspiration book.