The DO 9721 quantum photo-radiometer and thermometer data logger has been designed for measuring illuminance, irradiance, luminance and temperature. The instrument has two inputs, A and B, and automatically detects the sensors, whether illuminance, irradiance, luminance or temperature and can provide a view of the difference between the two inputs. As the probes are interchangeable, it is possible to choose the most suitable combination for all applications without having to recalibrate the instrument. The DO 9721 can take illuminance measurements in lux and in fcd (foot-candle), irradiance measurements in W/ m2, in μW/cm2 and in μmol·m-2s-1, luminance measurements in cd/m2 and temperature measurements in °C or °F. Function as datalogger: 30,000 samples, REL, Record, Q (integration), RS232C serial output. LP9021.. series probes complete with electronics are suitable. The probes and cables for data download (9CPRS232 or C205) have to be ordered separately.