Question: UV Sensor SEN00700P Signal Voltage

Hi! We got an UV sensor SEN00700P board powered with 3.3V, the measured output signal voltage was about 271mV in indoor environment. When we moved to outdoor, the signal voltage turned to 297mV.

If the board is powered with 5V, the measured voltage turns to 291mV indoor.

Does the data make any sense? and how to convert the voltage to illumination intensity such as uW/cm^2

Many thanks!