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.
大概在1800年 Humphry Davy第一次展示了仅用灯丝来发光的电灯
Bare filament electric lamps were first demonstrated around 1800 by Humphry Davy,
and the glass bulb was added later to keep oxygen away from the wire
so it could glow for a long time without actually burning up.
So the incandescent light bulb is 19th-century technology,
and by now there’s now a blinding array of electric lamps:
像卤素灯 荧光灯 汞钠蒸气灯 LED灯 激光等
halogen light bulbs, fluorescents, mercury and sodium vapor lamps, LEDs, lasers and so on.
Each one makes its own clever use of physics to achieve the life goal of a light bulb:
converting electrical current into visible light.
Here’s how they work.
Halogen bulbs have the same tungsten metal filament as typical incandescent light bulbs,
but they contain a little bit of a halogen-based gas in the bulb as well.
The chemistry of the halogen gas allows it to capture stray tungsten atoms that evaporate off the filament
and shepherd them back to where they belong,
which both prolongs the life of the filament as well as keeps the inside of the bulb clean and clear.
Fluorescent bulbs are basically gas-filled tubes with electrodes at both ends.
Electrical current flows from one electrode to the other,
and when the electrons that make up the current bump into mercury atoms in the gas,
the energy of the collision makes the atoms get “excited”—that’s the technical term
—and the atoms then emit visible and ultraviolet light.
The white coating on the inside of the glass absorbs the ultraviolet light and re-emits it as more visible light
—this process is called “fluorescence” and is the namesake of the bulbs.
Because the coating stops the UV light, it also keeps the bulbs from giving you cancer…
unless that’s what you want, in which case you can use a tanning bulb with a different kind of coating.
Sodium, mercury, and metal-halide vapor lamps, which are commonly used for lighting streets,
仓库 体育场馆和其它大场地的照明 这些灯都是让电流穿过气体而发光的
warehouses, gymnasiums, and other large areas, are also tubes that run electrical current through a gas.
The gas itself emits mainly visible light so these bulbs don’t need a fluorescent coating.
最后一种灯 LED灯 它与荧光灯类似
Finally, LEDs are also like fluorescent light bulbs,
除了它不用气体 而是用细小的半导体镓晶体做媒介 可以不必有外面的灯泡
except replace the gas with a tiny crystal of semiconducting gallium, and throw away the bulb
—so not like fluorescent bulbs.
但是仔细观察就会发现 这个半导体晶体有两层 一层是为活跃电子提供更多的能量
But seriously, the semiconductor has two layers, one of which provides excited electrons with lots of energy,
while the other provides a place for the electrons to go and relax
—and that *is* the technical term.
All you need is an electrical current to transport electrons from the party side to the spa side
where they release the energy of their excitement as light.
看 这个是发光二极管 特别适合在派对时用
Voilá – a light-emitting diode, perfect for human parties!