Digital Photometer/Radiometer Features Digital LED Readout Eight Silicon Sensor Probes Quickly Interchange Without Recalibration Accurate Spectral and Cosine Corrections AC or Internal Rechargeable Battery Versions Display: 3½ digit LED readout and three LEDs automatically indicating correct units for probe in use Integration Time: approx. 100 ms Mainframe has internal rechargeable NiCad batteries that require 16 hours for a full charge. For continuous-operation an ac power supply is recommended.