In the manufacturing of semiconductor products, there is a variation of performance around the average values given in the manufacturers technical data sheets. For this reason, manufacturers bin the LED components for luminous flux, forward voltage and colour frequency. Specific bin LEDs are available for purchase at additional cost for applications where consistency across units is critical.
Some high quality fixture manufactures (Chroma-Q for example) have developed technology to adjust for variances in luminous flux and forward voltage between batches of LED. Regarding colour frequency, the human eye is most sensitive to colour frequency variance around the green/yellow (550nm) area and Chroma-Q LED fixtures are manufactured with the most tightly binned LEDs available (5nm) around this area. It should be noted that some people can still detect a slight variance within the 5Nm tolerance.
LED Performance Over Time
One of the strongest propositions of power Light Emitting Diodes (LEDs) is their long lumen maintenance - their ability to continue producing light output for many years of use, in contrast to most conventional light sources, which force users to go through repeated and frequent failure-and-replacement cycles.
LEDs experience a gradual reduction in light output during operation. This phenomenon is called light output degradation, and may stem either from a reduction in the light-emitting efficiency of the LED chip or a reduction in the light transmission of the optical path within the LED package. However, noting that the light output of an LED tends to degrade gradually as the device is stressed, its efficacy may fall to an unacceptable level long before total failure occurs. Such a condition may be described as a lumen maintenance failure. An LED with a lamp life quoted as up to 50,000 hours L70, should expect that 50% of units will have less than 70% of their initial output.
It is unlikely that all colours in a colour mixing LED fixture will have equal usage. It is therefore likely that a colour mixing LED fixture will become less able to deliver consistently accurate mixed colours after significant usage.
50,000 hours is equivalent to 6 years usage at 24 hours a day, 7 days a week. In a typical production environment a fixture may be used around 3 hours a day, 6 days a week, which is less than 1,000 hours a year.
Many LED fixtures incorporate LED engines with a lamp life quoted as up to 50,000 hours L70. Other components inside the fixtures have significantly shorter anticipated life therefore lamp life should not be misinterpreted as a likely life of the product as a whole.