虽然白炽灯的发光效率极限是每瓦52流明，然而这钨丝在其熔点的理论亮度。
While the upper limit for incandescent lamps is 52 lumens per watt, that is the theoretical luminosity of tungsten at its melting point.
同时，它高效的性能使之即便在接近寿命极限时，仍能保持百分之七十的亮度。
At the same time, its efficient performance can even close to life time, still can maintain seventy percent brightness.
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