Most lux sensors has a limited range ( < 100 000 lux ) and I plan a different approach.

Current source current is directly proportional to the solar radiation

Measuring Solar Radiation, Chuck Wright

In a solar cell, the parameter most affected by an increase in temperature is the open-circuit voltage -2.2 mV/°C

The short-circuit current, Isc, increases slightly with temperature, since the band gap energy, EG, decreases and more photons have enough energy to create e-h pairs. However, this is a small effect and the temperature dependence of the short-circuit current from a silicon solar cell is

A change form 25 to 50 °C will increase Isc current 1.5%.

The impact of increasing temperature is shown in the figure below

http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current

http://www.pveducation.org/pvcdrom/solar-cell-operation/effect-of-temperature

Pyranometers and reference cells
Pyranometers and Reference Cells, What’s the Difference ?