The Environmental Radiant Flux (ERF) detector has been devised for measurement of the radiant field including solar radiation indoors and outdoors. First, three assumptions set on the measurement principle have been studied. The first assumption of the uniform back surface temperature of the sensor elements is considered to be effected depending on so much thermal conductivity and heat content of the substrate as aluminum. The second of the uniform local heat transfer coefficient on the sensor surfaces is expected to be realized indoors, despite under 4 % in relative error in the case of 5 meters per second outdoors. The third of the uniform thermal conductance of the sensor elements is valid enough. Next, the study on the meter constant makes it clear to reduce the error of measurement with getting a large electric motive force, which is realized with a number of winding of thermocouple wire. The calibration system for the ERF detector is also shown. Regarding the effective solar absorptance of the three elements ERF detector, it has a system that, after calibration by artificial light, the constants are modified in the light of solar radiation. Based on the detailed study the calibration constants in artificial light are shown to be larger than those in solar radiation.
