Physics
PASPORT Light Level Sensor
Can be used as an absolute reference by detecting and measuring light in LUX.
The Light Level Sensor measures illuminance in lux. The readings of this sensor mimic the wavelength sensitivity of the human eye, which is most sensitive in the green portion of the spectrum. This is achieved with a green filter in the light sensor.
https://www.pasco.com/products/sensors/pasport/ps-2177#specs-panel