交通信號燈爲何用紅色 黃色和綠色

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 thataside from a hunch that it had to do with wavelengths, I had no idea myself, soI decided to look into it.

紅燈停，綠燈行，黃燈亮了快點走，但爲什麼交通信號燈要用這三個顏色，而不用藍色、紫色或者褐色呢？必須承認除了直覺認爲這與波長有關外，我完全不知道原因，所以我決定一探究竟。

The answer, as it turns out, is a littleconvoluted, but makes sense.

事實證明，答案確實有點複雜，不過倒也還講得通。

The earliest traffic signals were designedfor trains, not cars.

最早的交通信號燈是爲火車而不是汽車通行設計。

They were red and green, gas-powered, andmore than a little dangerous in the event of a leak.

信號燈爲紅色和綠色，使用煤氣，在漏油時會非常危險。

•Red is an inherited symbol from railroads

紅色源於鐵路信號燈

Red symbolizes danger in many cultures,which makes sense, considering it has the longest wavelength of any color onthe visible spectrum, meaning you can see it from a greater distance than othercolors.

由於紅色在可見光譜中波長最長，因此可視距離要比其它顏色更遠，這就可以理解爲什麼很多文化中將紅色視爲危險信號。

Red has meant stop since long before carsexisted, with train signals' use of red dating back to the days when mechanicalarms lifted and lowered to indicate whether the rail ahead was clear.

紅色很早以前就被用作火車信號，那時汽車還沒出現，而鐵路用機械臂板上升下降來代表前方是否有火車駛來。

So that one's simple.

這比較容易理解。

•Green meant "caution" at first

綠色最早用於警示

Green's role in lights has actually changeddramatically over time.

長期以來綠色在交通信號燈中的角色發生了巨大變化。

Its wavelength is next to (and shorterthan) yellow's on the visible spectrum, meaning it's still easier to see thanany color other than red and yellow.

可見光譜中，綠色波長因僅次於黃色，因此是除了紅色和黃色外最容易看見的顏色。

Back in the early days of railway lights,green originally meant "caution," while the "all-clear"light was, well, clear or white.

在早期的鐵路信號燈中，綠色最初代表警示，而無色或白色代表全線通行。

Trains, of course, take an interminablylong time to stop, and legend has it that several disastrous collisionshappened after an engineer mistook stars in the night horizon for an all-clear.

當然，火車停下來需要非常長的時間，據說由於一名工程師將夜晚天空中的星星誤認爲全線通行的信號燈，導致了若干起災難性事故的發生。

Thus, green became "go," and fora long time, railways used only green and red to signal trains.

因此，綠燈成爲了通行的標誌，長期以來鐵路也只將紅色和綠色作爲信號燈。

•Yellow means "caution" because it's almost as easy to seeas red

黃色代表注意，因爲它幾乎和紅色一樣顯眼。

From the earliest days of motoring up untilthe mid-1900s, not all stop signs were red --many were yellow, along with yieldsigns, because at night it was all but impossible to see a red stop sign in apoorly lit area.

從最早開始出現汽車到20世紀中期，並不是所有的停車信號都用紅色——很多使用黃色，讓路標誌也是，因爲夜晚在光線極暗的地方根本看不見紅色的停車信號。

The yellow stop-sign craze began in Detroitin 1915, a city that five years later installed its first electric trafficsignal, which happened to include the very first amber traffic light, at thecorner of Michigan and Woodward Aves.

黃色停車信號潮始於1915年的底特律，五年後，這座城市在密歇根和伍德沃德大街安裝了第一個首次包括黃色燈的電子交通信號燈。

But what of those weird yellow stop signs,you ask? As materials and technologies evolved, the ability to produce highlyreflective signs meant that red could resume its natural spot in the signhierarchy, leaving the still-highly-visible yellow (it's second only to red interms of visible wavelength) to the domain of "caution." That's whyschool zones and buses, crosswalks, and other important warnings are yellowtoday.

你是不是想問，那些奇怪的黃色停止標誌又是幹什麼的呢？材料學和高技術的發展使得人們研發出高度反光指示燈，因此紅色才能在信號燈中重拾停車霸權，將可視度較高的黃色（可視波長僅次於紅色）留在了警告的位置。這也是爲什麼學校區、公交站、人行橫道和其它重要位置使用黃色警告信號燈的原因。