UL 60079-28 2017 pdf download – Explosive Atmospheres – Part 28: Protection of Equipment and Transmission Systems Using Optical Radiation.
5.2.2.2 Optical power If compliance with Table 2, Table 3 or Table 4 is to be based on maximum optical power values, then maximum optical power shall be measured in accordance with one of the following test methods, using the same or equivalent thermal dissipation conditions as in the intended application: 1) The actual driver circuitry is used to power the optical device, with maximum optical power measured under fault conditions in accordance with the over-power / energy fault protection criteria according to 5.2.5 and the respective EPL at ambient temperature between 21 °C and 25 °C. If the optical power is higher at the foreseen ambient temperature range of the equipment, the measured value at room temperature shall be adjusted according to the temperature coefficient taken from the data sheet. If no information is given in the data sheet then the measurement shall be done additionally in the lowest and highest values of the temperature range specified for the equipment. Separate samples shall be taken for each of the 3 tests if the optical device is subjected to input parameters which are higher than its maximum rating. The number of test samples depends upon the number of fault conditions to be applied. 2) The maximum input parameters to the optical device from the actual driver circuitry are calculated based on analysis of the driver circuitry schematic. This analysis shall include consideration of fault conditions in accordance with the over-power / energy fault protection criteria according to 5.2.5 and the respective EPL. One test sample of the optical device without the driver circuitry is then connected to a separate variable source of supply and subjected to input parameters equal to the maximum calculated input parameter values. Maximum optical power is measured with the optical device at ambient temperature between 21 °C and 25 °C.