The present invention provides a probe (I) 14 measuring loss of radiative heat flux from combustion systems. The present probe (I) consists of a stainless steel cylindrical body member (2) and (3), a copper disc (5), a thermal insulation (7) provided between the copper disc (5) and a body member (2) and (3), a quartz plate (4) acting as a front window of the probe (1), a thermocouple (8) is brazed at centre of copper disc (5) 14 measuring voltage variation with radiative heat flux transiZT. The present probe (1) is vertically positioned in cone calorimeter (10) cinll calibrated for different radiative heat flux levels. A data acquisition system (12) is used to continuously record the measured voltage variation values by which loss of radiative heat flux from combustion systems is measured.