I discussed photosynthetically active radiation during a seminar this week in Tokyo.

This slide showed the distribution of the daily light integral (DLI) in Tokyo during 2014 on days with an average temperature greater than or equal to 20°C.

I mentioned that one could make an overlay of the distribution of DLI at other locations, and that a distinctive feature of the Tokyo-area climate is that there will be more days with a low DLI than at locations with a similar temperature in the southeastern USA.

In this plot, I show the density of DLI in 2014 for Tokyo and Watkinsville.

The temperatures in these locations were similar in 2014; the mean of the mean daily temperatures was 16°C in Watkinsville and 16.8°C in Tokyo. There were 151 days in 2014 with mean daily temperature >= 20°C in Watkinsville; Tokyo had 150 such days.

For the DLI on those days, however, there is quite a difference. The median DLI for those 150 days in Tokyo was 35.8, compared to 42.1 in Watkinsville.