Peak UVI vs Peak Lux

Remarkably consistent peak UV readings (green) during periods of clear sky in contrast to a dramatic difference in measured cumulative average LUX per hour. The bulk of the energy received occurred during the morning both days.

The morning of the 14th was bright and clear with some clouds in the afternoon.

The 15th was fairly overcast with the exception of a narrow mid-morning window of sun trying to break through the clouds.

For the top chart, the green trace is interior measured UVI, the orange trace is an outside clear-sky model for UVI. The interior UV sensor was positioned normal to the peak sunlight.