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    LED lamp really reach 50000 hours?

    How long is 50,000 hours?
    There are 8,760 hours in a year, so here's what 50,000 hours works out to be, depending on lamp hours of operation.

    Hours of Operation:
    24 hours a day 5.7 years
    18 hours per day 7.6 years
    12 hours per day 11.4 years
    8 hours per day 17.1 years

    Why is the life span of an LED measured as lumen depreciation?
    The life span of an LED is vastly longer than that of incandescent, fluorescent or HID lamp sources, generally lasting 50,000 hours or longer. Although the LED never really burns out, product life span is measured by lumen depreciation.

    The Illuminating Engineering Society's (IES) current standard for calculating the life of an LED as the point at which the LED reaches 30 percent lumen depreciation.

    Remember, a 100,000-hour rating is not equivalent to lamp life rating. LED life is rated where it has reached 30 percent lumen depreciation. At 100,000 hours an LED would still be operating, but at a decreased lumen output.

    What is junction temperature?
    Junction temperature is the temperature at the point where an individual diode connects to its base. Maintaining a low junction temperature increases output and slows LED lumen depreciation. Maintaining a low junction temperature is critical for evaluating an LED product's quality and ability to deliver long life.

    What can affect the LED junction temperature?
    There are three things which can affect the junction temperature of LED’s: drive current, thermal path and ambient temperature. In general, the higher the drive current, the greater the heat generated at the junction. Heat must be moved away from the junction in order to maintain expected light output, lifespan and color. The amount of heat that can be removed depends upon the ambient temperature and the design of the thermal path from the junction to the surroundings. Typically the junction temperature should be maintained below 120°C.

    Lumen depreciation in LEDs varies depending on package and system design. The primary cause of lumen depreciation is heat generated at the LED junction. LEDs do not emit heat as infrared radiation (IR) like other light sources, so the heat must be removed from the device by conduction or convection. If the LED system design has inadequate heat sinking or other means of removing the heat, the device temperature will rise, resulting in lower light output. Clouding of the epoxy encapsulant used to cover some LED chips also results in decreased lumens making it out of the device. Newer high-power LED devices use silicone as an encapsulant, which prevents this problem. LEDs continue to operate even after their light output has decreased to very low levels. This becomes the important factor in determining the effective useful life of the LED.

    When we talking about lifespan of LED, it refers to L70 which is when the lumen maintenance is 70% of the original level. Generally it is not convenient to test a LED lamp continuously for 50000 hours. So generally the lab will using accelerated aging test method to get the lumen depreciation situation after 6000 hours or 10000 hours , together with Decay curve fitting, to evaluate lifespan of LED. Currently there are two main standards of testing lumens depreciation, they are LM79 and TM-21. When the test reports meet standards of 50000 hours requirement, we can state the life span of the LED lamp reach 50000 hours.

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