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Light bulbs used to be simple: just run a bunch of electrical current through a thin wire until it heats up enough to start glowing.
以前的灯泡很简单：只是让一束电流通过一根细电线，直到它足够热并开始发光。
Bare filament electric lamps were first demonstrated around 1800 by Humphry Davy,
1800年左右，汉弗莱·戴维首次展示了白炽灯，
and the glass bulb was added later to keep oxygen away from the wire
并且后来又加了玻璃灯泡，以防止氧气接触电线
so it could glow for a long time without actually burning up.
这样它可以长时间发光而不会真正烧起来。
So the incandescent light bulb is 19th-century technology,
白炽灯泡是19世纪的技术，
and by now there's now a blinding array of electric lamps:
并且现在已经有了很多令人眼花缭乱的电灯：
halogen light bulbs, fluorescents, mercury and sodium vapor lamps, LEDs, lasers and so on.
卤素灯泡、荧光灯、水银灯和钠蒸汽灯、LED灯、激光灯等等。
Each one makes its own clever use of physics to achieve the life goal of a light bulb:
每一种都巧妙地运用了物理学来实现灯泡的生活目标：
converting electrical current into visible light. Here's how they work.
将电流转换成可见光。它们是这样运作的。
Halogen bulbs have the same tungsten metal filament as typical incandescent light bulbs,
卤素灯泡和典型的白炽灯泡使用相同的钨金属丝，
but they contain a little bit of a halogen-based gas in the bulb as well.
但是灯泡里也含有一些卤素气体。
The chemistry of the halogen gas allows it to capture stray tungsten atoms that evaporate off the filament
卤素气体的化学性质使它能够捕获从灯丝上蒸发掉的钨原子，
and shepherd them back to where they belong,
并引导它们回到原来的位置，
which both prolongs the life of the filament as well as keeps the inside of the bulb clean and clear.
这既延长了灯丝的寿命，又保持了灯泡内部的清洁和清澈。
Fluorescent bulbs are basically gas-filled tubes with electrodes at both ends.
荧光灯基本上是两端都有电极的充气管。
Electrical current flows from one electrode to the other,
电流从一个电极流向另一个电极，
and when the electrons that make up the current bump into mercury atoms in the gas,
组成电流的电子与气体中的汞原子碰撞时，
the energy of the collision makes the atoms get 'excited'—that's the technical term
碰撞的能量使原子得到“激发——这是技术术语
—and the atoms then emit visible and ultraviolet light.
——然后原子便发出可见光和紫外线。
The white coating on the inside of the glass absorbs the ultraviolet light and re-emits it as more visible light
玻璃内部的白色涂层吸收紫外线，并将其重新发射为更多的可见光
—this process is called 'fluorescence' and is the namesake of the bulbs.
——这一过程被称为‘荧光’，与这种灯泡同名。
Because the coating stops the UV light, it also keeps the bulbs from giving you cancer...
因为这种涂层可以阻挡紫外线，也可以防止灯泡致癌……
unless that's what you want, in which case you can use a tanning bulb with a different kind of coating.
除非这是你想，在这种情况下，你可以使用一种不同涂层的鞣制灯泡。
Sodium, mercury, and metal-halide vapor lamps, which are commonly used for lighting streets,
钠、汞和金属卤化物蒸汽灯通常用于照明街道、
warehouses, gymnasiums, and other large areas, are also tubes that run electrical current through a gas.
仓库、体育馆和其他大面积区域，它们也是通过气体输送电流的管道。
The gas itself emits mainly visible light so these bulbs don't need a fluorescent coating.
这种气体本身主要发出可见光，所以这些灯泡不需要荧光涂层。
Finally, LEDs are also like fluorescent light bulbs,
最后，LED灯也像荧光灯一样，
except replace the gas with a tiny crystal of semiconducting gallium, and throw away the bulb —so not like fluorescent bulbs.
除了前者只是用一小块半导体镓晶体代替了气体，然后把灯泡扔掉了——所以它不像荧光灯。
But seriously, the semiconductor has two layers, one of which provides excited electrons with lots of energy,
但说正经的，半导体有两层，其中一层为激发电子提供大量能量，
while the other provides a place for the electrons to go and relax —and that is the technical term.
而另一层则为电子提供了一个自由活动和放松的空间——这是一个技术术语。
All you need is an electrical current to transport electrons from the party side to the spa side
你所需要的只是一股电流，将电子从派对的一侧传输到另一侧，
where they release the energy of their excitement as light.
在那里，电子以光的形式释放出兴奋的能量。
Voila - a light-emitting diode, perfect for human parties!
一个发光的二极管，完美适用于人类的聚会！
