Life and Lumen Maintenance

Traditionally the rated lamp life of light sources is defined as an average rating, in hours, for the time it takes 50% of a large group of the lamps to fail (B50).

However, this rating is purely based on lamp survival and does not take into account lumen depreciation. An additional way of measuring lamp life is therefore required for LEDs, which can have extremely long lives.

To measure the lumen depreciation, an LED is tested under normal operating conditions and the lumen output of the lamp is measured at 6,000 hours. This measurement is then compared to the initial output of the lamp and the depreciation of lumen output calculated- see Energy Star table. This is then extrapolated on a lumen maintenance curve- see graph.

The resultant curve shows the amount of remaining luminous lux output- expressed as a percentage of the initial output- at any selected elapsed operating time. This data then makes it possible for manufacturers to provide a relative lumen output calculation over a lamps’ life and, importantly, to be able to indicate the point at which an LED will be operating at an output level that is not considered viable in terms of light quality. This point is called the rated lumen maintenance life (Lxx) and shows the elapsed operating time at which a specified percentage of lumen maintenance is reached - this is expressed in hours. To illustrate this, if an LED has a rated lumen maintenance life of L70 at 40,000 hours, then it will operate for 40,000 hours before falling below 70% of its initial light output level.

MEGAMAN^® quotes this L70 number for all LED products which is the expected time when used in normal open conditions for the unit to reach 70% lumen maintenance andthe end of useful life. MEGAMAN^® also tests all LEDs in the most onerous conditions, for example to simulate use in enclosed fixtures, and calculate a minimum rated life. Both rated life and L70 life are quoted on the product pages.

MEGAMAN^® has an ongoing program for long term life test of professional LED’s. Test measurements of lumen output are taken regularly to verify the projections of lumen maintenance and life. For this reason life claims may change and the product pages on this website should be referenced for the latest information.