交通信号灯为何用红色、黄色和绿色？

 　　Red means "stop," green means "go," and yellow means "hurry up and make that damn light." Why those colors, though? Why not blue, purple, and brown? I have to admit that aside from a hunch¹ that it had to do with wavelengths³, I had no idea myself, so I decided⁴ to look into it.

　　红灯“停”，绿灯“行”，黄灯亮了“快点走”，但为什么交通信号灯要用这三个颜色，而不用蓝色、紫色或者褐色呢？必须承认除了直觉认为这与波长有关外，我完全不知道原因，所以我决定一探究竟。

　　The answer, as it turns out, is a little convoluted⁵, but makes sense. The earliest traffic signals were designed for trains, not cars. They were red and green, gas-powered, and more than a little dangerous in the event of a leak.

　　事实证明，答案确实有点复杂，不过倒也还讲得通。最早的交通信号灯是为火车而不是汽车通行设计。信号灯为红色和绿色，使用煤气，在漏油时会非常危险。

　　交通信号灯为何用红色、黄色和绿色？

　　? Red is an inherited symbol from railroads

　　红色源于铁路信号灯

　　Red symbolizes⁶ danger in many cultures, which makes sense, considering it has the longest wavelength² of any color on the visible spectrum⁷, meaning you can see it from a greater distance than other colors. Red has meant stop since long before cars existed, with train signals' use of red dating back to the days when mechanical arms lifted and lowered to indicate whether the rail ahead was clear. So that one's simple.

　　由于红色在可见光谱中波长最长，因此可视距离要比其它颜色更远，这就可以理解为什么很多文化中将红色视为危险信号。红色很早以前就被用作火车信号，那时汽车还没出现，而铁路用机械臂板上升下降来代表前方是否有火车驶来。这比较容易理解。

　　? Green meant "caution" at first

　　绿色最早用于“警示”

　　Green's role in lights has actually changed dramatically over time. Its wavelength is next to (and shorter than) yellow's on the visible spectrum, meaning it's still easier to see than any color other than red and yellow. Back in the early days of railway lights, green originally meant "caution," while the "all-clear" light was, well, clear or white. Trains, of course, take an interminably long time to stop, and legend has it that several disastrous⁸ collisions happened after an engineer mistook stars in the night horizon for an all-clear. Thus, green became "go," and for a long time, railways used only green and red to signal trains.

　　长期以来绿色在交通信号灯中的角色发生了巨大变化。可见光谱中，绿色波长因仅次于黄色，因此是除了红色和黄色外最容易看见的颜色。在早期的铁路信号灯中，绿色最初代表“警示”，而无色或白色代表“全线通行”。当然，火车停下来需要非常长的时间，据说由于一名工程师将夜晚天空中的星星误认为全线通行的信号灯，导致了若干起灾难性事故的发生。因此，绿灯成为了“通行”的标志，长期以来铁路也只将红色和绿色作为信号灯。

　　? Yellow means "caution" because it's almost as easy to see as red

　　黄色代表“注意”，因为它几乎和红色一样显眼。

　　From the earliest days of motoring up until the mid-1900s, not all stop signs were red --many were yellow, along with yield signs, because at night it was all but impossible to see a red stop sign in a poorly lit area. The yellow stop-sign craze began in Detroit in 1915, a city that five years later installed its first electric traffic signal, which happened to include the very first amber⁹ traffic light, at the corner of Michigan and Woodward Aves.

　　从最早开始出现汽车到20世纪中期，并不是所有的停车信号都用红色——很多使用黄色，让路标志也是，因为夜晚在光线极暗的地方根本看不见红色的停车信号。“黄色停车信号潮”始于1915年的底特律，五年后，这座城市在密歇根和伍德沃德大街安装了第一个首次包括黄色灯的电子交通信号灯。

　　But what of those weird¹⁰ yellow stop signs, you ask? As materials and technologies evolved, the ability to produce highly reflective signs meant that red could resume its natural spot in the sign hierarchy¹¹, leaving the still-highly-visible yellow (it's second only to red in terms of visible wavelength) to the domain¹² of "caution." That's why school zones and buses, crosswalks, and other important warnings are yellow today.

　　你是不是想问，那些奇怪的黄色停止标志又是干什么的呢？材料学和高技术的发展使得人们研发出高度反光指示灯，因此红色才能在信号灯中重拾“停车霸权”，将可视度较高的黄色（可视波长仅次于红色）留在了“警告”的位置。这也是为什么学校区、公交站、人行横道和其它重要位置使用黄色警告信号灯的原因。

1 hunch   

n.预感，直觉

参考例句：

• I have a hunch that he didn't really want to go.我有这么一种感觉，他并不真正想去。
• I had a hunch that Susan and I would work well together.我有预感和苏珊共事会很融洽。

2 wavelength   

n.波长

参考例句：

• The authorities were unable to jam this wavelength.当局无法干扰这一波长。
• Radio One has broadcast on this wavelength for years.广播1台已经用这个波长广播多年了。

3 wavelengths   

n.波长( wavelength的名词复数 )；具有相同的/不同的思路；合拍；不合拍

参考例句：

• I find him difficult to talk to—we're on completely different wavelengths. 我没法和他谈话，因为我们俩完全不对路。 来自《简明英汉词典》
• Sunlight consists of different wavelengths of radiation. 阳光由几种不同波长的射线组成。 来自辞典例句

4 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

5 convoluted   

adj.旋绕的；复杂的

参考例句：

• The snake slithered through a convoluted path.蛇在羊肠小道上爬行。
• The policy is so convoluted even college presidents are confused.这项政策太令人费解，甚至连大学校长们也是一头雾水。

6 symbolizes   

v.象征，作为…的象征( symbolize的第三人称单数 )

参考例句：

• The use of light and dark symbolizes good and evil. 用光明与黑暗来象征善与恶。
• She likes olive because It'symbolizes peace. 她喜欢橄榄色因为它象征着和平。 来自《简明英汉词典》

7 spectrum   

n.谱，光谱，频谱；范围，幅度，系列

参考例句：

• This is a kind of atomic spectrum.这是一种原子光谱。
• We have known much of the constitution of the solar spectrum.关于太阳光谱的构成，我们已了解不少。

8 disastrous   

adj.灾难性的，造成灾害的；极坏的，很糟的

参考例句：

• The heavy rainstorm caused a disastrous flood.暴雨成灾。
• Her investment had disastrous consequences.She lost everything she owned.她的投资结果很惨，血本无归。

9 amber   

n.琥珀；琥珀色；adj.琥珀制的

参考例句：

• Would you like an amber necklace for your birthday?你过生日想要一条琥珀项链吗？
• This is a piece of little amber stones.这是一块小小的琥珀化石。

10 weird   

adj.古怪的，离奇的；怪诞的，神秘而可怕的

参考例句：

• From his weird behaviour,he seems a bit of an oddity.从他不寻常的行为看来，他好像有点怪。
• His weird clothes really gas me.他的怪衣裳简直笑死人。

11 hierarchy   

n.等级制度；统治集团，领导层

参考例句：

• There is a rigid hierarchy of power in that country.那个国家有一套严密的权力等级制度。
• She's high up in the management hierarchy.她在管理阶层中地位很高。

12 domain   

n.(活动等)领域，范围；领地，势力范围

参考例句：

• This information should be in the public domain.这一消息应该为公众所知。
• This question comes into the domain of philosophy.这一问题属于哲学范畴。