They may have to do so by 2020, when all general-purpose bulbs sold in America will have to produce 45 lumens per watt.

美国人可能不得不在2020年开始全面使用CFLs灯和LEDs灯，到那时在美国出售的所有一般用途的灯泡都必须产生每瓦45流明的亮度。

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If people want to replace their old power-hungry incandescent bulbs with CFLs or LEDs good for 45 lumens per watt, all the better.

如果人们想要把他们的高耗能白炽灯换成45每瓦流明的CFLs灯或者LEDs灯，那就再好不过了。

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While the upper limit for incandescent lamps is 52 lumens per watt, that is the theoretical luminosity of tungsten at its melting point.

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。

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Cree already advertises an LED lamp it says reaches 200 lumens per watt under some circumstances.

NPR: Goodbye Fluorescent Bulb? Philips Says Yes.

And it is squeezing brighter images from its projectors, a feature measured in lumens per watt.

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U.S. Department of Energy projections published in April 2012 showed the government had expected the industry would only achieve efficiencies of 160 lumens per watt for LED lamps by 2015.

NPR: Goodbye Fluorescent Bulb? Philips Says Yes.