To determine the L and B values, the luminous flux of an LED is measured over at least 6,000 hours according to the IES LM-80 standard. Then, according to the IES TM-21 standard (Projecting Long Term Lumen Maintenance of LED Light Sources), it is extrapolated to a maximum of 6 times the measurement duration according to LM-80. To obtain values for 50,000 operating hours, at least 50,000 / 6, i.e. around 8,334 hours, must be measured. For comparison: one year of continuous operation corresponds to 8730 hours.
For some LED types, there are now also valid measurements that can be used to calculate a forecast for 100,000 hours. The forecasts are based on certain operating conditions, e.g. ambient temperature and current applied. For example, luminous flux maintenance can be significantly extended beyond the forecast period with a lower LED current flow and optimised thermal management.