Chart of the week: photosynthetically active radiation

On a sunny day with no clouds, the photosynthetically active radiation (PAR) that the grass receives on the earth's surface can be calculated from the latitude and longitude of any location. I calculated this for the 15th of each month for the location of Purdue University in Indiana. The values of photosynthetic photon flux density (PPFD) are what the PPFD would be for one second in a full sun hour at that location on that date.

The PPFD ranges from…