It is important to get know well of lumen first. As usually, we refer to the amount of light emitted by the LED light source per unit time as the luminous flux, unit: lumen, LM. The amount of light is for light source, description of size of the total amount of light emitted by the light source, equivalent to the luminous power, and greater the luminous flux of the light source, the more light is emitted. When a luminaire ignites under specified conditions, the ratio of the luminous flux at a particular time during the life of the lamp to that of the initial of the lamp, expressed as a percentage. The luminous flux will be decreasing as increasing ignition time, so the effective life is defined by the lumen maintenance rate. When the luminous flux maintenance rate is lower than 50%, it can be regarded as the lamp has reached the service life, but the national standard requires the lumen maintenance rate of 2000H to be not less than 78%, the advanced level in foreign countries requires not less than 90% on same situation; the standard of the US Energy Star is that the lumen maintenance rate is not less than 80% at 40% of rated life.
A noun refers to “light degradation”, corresponding to the lumen maintance, of which is inversely proportional each other. The light degradation of LED is mainly affected by the following two factors:
1. LED quality: LED chip in it is not good, and brightness is attenuation in a faster speed. There exsits defect craft during production, and the heat dissipation of the LED chip cannot be well derived from the PIN pin, resulting in an excessive temperature of the LED chip, which intensifies the chip attenuation.
2. Using surroundings: The LED is driven by a constant current, and some of the LEDs are driven by voltage, which will make the LED attenuate faster. Obviously, the lumen maintenance rate is the core factor for judging the advantages and disadvantages of LED light sources.
