With LEDs the luminous flux decreases over time, as the diodes are used. This light depreciation is more or less linear across the diode’s service life. The luminaire itself can compensate for this light depreciation using a programmable driver. This is known as Constant Light Output (CLO).
The L-value describes the light depreciation of diodes over time. Thus, a CLO luminaire with L100 ensures the diodes have the same light level after 50,000 hours of burn time as when they were first installed. By contrast, an L80 luminaire has lost 20% of its original light level.
What are the benefits of Constant Light Output (CLO)?
CLO luminaires with L100 increase the maintenance factor, contributing towards more optimised and sustainable facilities. The optimisation is made possible by reducing over illumination. Less over illumination results in less installed output and, in some cases, can even require fewer luminaires. Ultimately saving energy – a benefit for both the environment and your finances.
How is L100 created?
A luminaire receives a constant luminous flux, or L100, by means of pre-programming the power supply to increase over a specified time. By using this arrangement, the increase in power compensates for the diodes’ light depreciation. The L-value applies to the luminaire as a whole, although the diodes themselves vary in light level. Since the ballast is set to gradually increase in watts and meet the variation of the diodes, the L-value always remains at 100 for a predetermined time.
Calculating the maintenance factor
A high L-value is good, because it is the basis for the maintenance factor applied when planning the lighting. This is obtained by multiplying the L-value (i.e. the light depreciation) with the lamp survival factor, luminaire maintenance factor and the room surface maintenance factor.
The method for making this calculation is provided in the Lighting template, which also stipulates the values to be used in the formula. In our example, we have values for an open pendant office luminaire, in a cleaning interval of three years, with 500 lux after 50,000 h. Consequently, the luminaire with L80 maintenance factor has a maintenance factor of 0,71 and the luminaire with CLO and L100 a factor of 0,89.
|Light depreciation (LLMF)||x 0,80||x 1,00|
|Lamp Survival Factor (LSF)||x 1,00||x 1,00|
|Luminaire Maintenance Factor (LMF)||x 0,94||x 0,94|
|Room Surface Maintenance Factor (RSMF)||x 0,95||x 0,95|
|Maintenance Factor (MF)||= 0,71||= 0,89|
Do you wish to learn more?
Contact Fagerhult for more information.