How to get that old-fashioned light bulb glow without wasting so much energy
一种全新的白炽灯泡可以将原来浪费的红外光转变为有用的可见光
爱迪生听到这个消息一定会高兴得跳起来。因为科学家找到了一种非常棒的提高爱迪生白炽灯灯泡发光效率的办法。
原来，爱迪生灯泡里的灯丝发出来的光有很大一部分是没有用的红外光，科学家们利用纳米工程技术制造了能回收这些红外光的镜子，这将令传统的爱迪生灯泡获得新生。（译者注：灯泡是用来给人看的。红外线看不见，完全是浪费！）虽然目前这种技术还没有商业化，但应用这项技术可以让白炽灯的发光效率达到达到目前LED等的水平。而且，这种灯泡发出的光芒，却不像LED等那样冷酷刺眼，保持了传统白炽灯那样的怀旧温暖色调。
各种光源消耗了美国11%的电力资源。任何改进光源用电效率的方法都会大幅度减少电的浪费或减轻影响全球气候的二氧化碳释放。
白炽灯在爱迪生商业化后就基本上没有改进过。电流穿过卷曲的钨制灯丝，灯丝的电阻让通过的电子把灯丝加热到3000K（K为开氏温度）。在这样的高温下，灯丝发出了人们喜爱的温暖的淡黄色光芒。
不过，仅仅2%的电能在穿过灯丝的时候变成可见光，大部分的能量都变成了波长更长的红外光，以热量的形式散失掉了。
正是因为爱迪生灯泡的这种低效率浪费了很多的电，人们就发明了其他类型的灯泡。例如节能灯(紧凑型荧光灯)，其发光效率为7%-13%；LED灯，其发光效率为5%-15%。但是，到目前为止，这些新品种灯都没办法像爱迪生的白炽灯那样让消费者喜爱，因为它的灯光是那样地让人感到温暖。
为了让白炽灯达到更高的用电效率，科学家们想办法制造纳米材料来把白炽灯的红外光转化为可见光，但由于灯泡的温度在通电后快速升高，这些纳米材料很快就被烤焦了，纳米结构也受到破坏。
麻省理工的科学家们（Ognjen Ilic, Marin Soljačić, and John Joannopoulos等）研究出了一种复杂结构的材料，叫做光子晶体（photonic crystal）。这种材料不怕灯丝的高热，既充当滤光片又充当反光镜（反射红外光，透过可见光）。这样，灯丝发出的红外光被反射回来，让灯丝再次吸收并重新发射可见光，而可见光则透过材料直接发射出去。（译者注：没变成可见光就别想跑出去！）
为了产生这种光子晶体，科学家采用1毫米厚的玻璃，在上面沉积了90层的氧化钽和二氧化硅。这两种金属氧化物的混合物可以选择性地反射红外光而透过可见光。沉积的厚度是根据计算机的模拟计算优化得到的。
钨灯丝也被重新设计了。原来细长卷曲的灯丝形状现在改成了来回折叠的彩带形状。电子同样因为灯丝的曲折而遇到了很高的电阻并施放很多的能量。但由于带状灯丝的表面积比较大，光子晶体反射回来的红外光能被很好地截住并吸收。
此项研究发表在Nature Nanotechnology。研究报告声称这种方法让传统的白炽灯的发光效率提高到原来的三倍以上，达到了6.6%。这还只是初步成果。在可预期的未来，其发光效率可能提高到惊人的40%。他们把这种技术叫做热光子伏打技术（thermophotovoltaics）。如果真的达到这个目标，这种高端纳米技术将让爱迪生灯泡的新版本再一次为人类带来温暖的光芒。
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原新闻稿： Science，DOI: 10.1126/science.aae0209
-----------英语学习------------
词汇:
incandescent light bulb: 白炽灯
filament: 灯丝
nanostructures: 纳米结构
tungsten: 钨
IR photons: 红外光光子
scorching: 灼热
英文原文:
How to get that old-fashioned light bulb glow without wasting so much energy
Thomas Edison would be pleased. Researchers have come up with a way to dramatically improve the efficiency of his signature invention, the incandescent light bulb. The approach uses nanoengineered mirrors to recycle much of the heat produced by the filament and convert it into additional visible light. The new-age incandescents are still far from a commercial product, but their efficiency is already nearly as good as commercial LED bulbs, while still maintaining a warm old-fashioned glow.
“This is beautiful work,” says Shawn-Yu Lin, an electrical engineer and optics expert at the Rensselaer Polytechnic Institute in Troy, New York. He and others note that there is plenty of room for further improving the mirrors, which could ultimately push the efficiency of the bulbs well beyond what is possible with today’s lighting technologies. And because lighting consumes 11% of all electricity in the United States, any such improvement could dramatically lower energy use, and, by extension, the carbon dioxide emissions that contribute to climate change.
Incandescent lights have changed little since Edison first perfected them. The bulbs work by sending electricity through a curly tungsten filament. The long, twisting path increases the electrical resistance faced by traveling electrons, heating the filament to some 3000 K. At that temperature, the filament glows with the warm yellowish white light that we’ve come to expect from light bulbs.
Still, only about 2% of the energy fed into an incandescent is emitted at visible wavelengths. Most of its output is at longer infrared (IR) wavelengths and is wasted as heat. Other technologies do somewhat better. Compact fluorescent bulbs typically reach an efficiency between 7% and 13%; LEDs manage between 5% and 15%. But so far, these types of bulbs have had trouble producing the warm white light that most consumers prefer.
Researchers have tried to boost the efficiency of some light emitters by sculpting the surface of the emitting material with nanostructures designed to emit more energy as visible light. But with incandescent bulbs, the tungsten filament’s scorching temperature quickly causes such nanostructures to fall apart.
Instead, researchers at the Massachusetts Institute of Technology (MIT) in Cambridge, led by physicists Ognjen Ilic, Marin Soljačić, and John Joannopoulos, set out to boost incandescent efficiencies with the help an intricately structured material, called a photonic crystal, that would sit apart from the filament and be more stable. Photonic crystals can act as both filters and mirrors, allowing some wavelengths of light to pass through while reflecting others. So the MIT team set out to create photonic crystals that would allow visible light to pass through while reflecting IR photons. The hope was that the filament would reabsorb the IR photons, which would then reemit some of that energy as visible light.
To create their photonic crystals, the researchers started with millimeter-thick sheets of glass and deposited 90 alternating layers of tantalum oxide and silicon dioxide. This mix was chosen because it reflects IR light but not visible photons. The team relied on extensive computer modeling to determine exactly how thick the layers had to be.
They also had to redesign the bulb’s tungsten filament. In place of the curly wire, they folded a thin tungsten ribbon back and forth, creating what looks like a thin tungsten sheet. Electrons still follow a long, circuitous path, ensuring that they face a high electrical resistance, and thus heat up the metal so it will glow. But the larger surface area of the tungsten sheet now makes it easier for the metal to absorb more IR photons reflected by the photonic crystals.
The team flanked the sheet like tungsten emitter with two sheets of the glass-coated photonic crystals and turned on the power. As they report today in Nature Nanotechnology, the crystals allowed virtually all the visible light to pass through but reflected the majority of IR photons back to the emitter , where they were reabsorbed. The energy recycling ultimately improved the efficiency of the bulb to 6.6%, triple that of conventional light bulbs.
That’s still at the lower end of the efficiency range for compact fluorescents and LEDs. However, “I think they can do even better than this,” says Alejandro Rodriguez, an electrical engineer and photonic crystal expert at Princeton University. Rodriguez notes that the MIT’s photonic crystal mirrors would likely be even more efficient at reflecting IR light if they included additional types of materials and more complex structures. Nevertheless, he says, “this is a nice first step.”
Ilic and Soljačić say with further engineering it may even be possible to reach efficiencies of 40%, far beyond what commercially available LEDs can muster today. They are looking at using a similar approach to improve the electrical conversion efficiency of devices called thermophotovoltaics, which use sunlight to heat tungsten so that it emits light at a wavelength that is efficiently converted to electricity by a solar cell. For either application to succeed, researchers must show that they can make and their photon recyclers cheaply enough to make them worth adding. If the approach lives up to its promise, cutting-edge photonics could give Edison’s glowing filaments a new lease on life.