Why are traffic lights round?

“Why are traffic lights round in shape?”, asked my toddler. As always, I excused myself saying”Dad is driving, no talking. I will explain it later”. So, I googled it and I was ready with the answer by the evening. I am sharing the findings here, so that you can save a couple hours of googling when your toddler asks you.

Traditionally the default the shape of traffic lights is round. Its like following a set up trend. But looking closely there are many benefits of round shapes. These are:

  1. Its more expensive to manufacture and maintain lights of different shape.
  2. If all the lights are of same shape, then same part can be used for any light. For example, the hood, glass etc. This saves a lot of inventory management. Imagine managing everything like inventory, orders etc of the thrice the volume as compared to today.
  3. Round shape provides a better protection against rain. The water is easily dissipated.
  4. Aerodynamically the round traffic lights are better against strong winds. They offer less resistance to wind.
  5. If you look at other light sources, such as bulb, LED, LCD etc, you will find that all of them are round in shape.This is because round shape is most stable. And you can’t have thick glass round the light.
  6. Round shape offers more reflection. So traffic lights are round for better light transmission.

Also you will notice that the order of the traffic light is similar everywhere. The default is Red to top, then yellow in middle and Green on bottom. For horizontally stacked lights this is Red on the left, then yellow in middle and Green at right. Although it is easy for normal people but the lights could get confusing for color blind people. This led to a odd shaped traffic light concept. This trend was known as UNISignal. In UNISignal, each light had its own shape. Red light is triangle shaped. Yellow light is round. Green light is square shaped. The order is lights in UNISignal is also Red, Yellow, Green from top to bottom or from left to right.

So we see that the traffic light are changing with time. There are many traffic signals where traditional traffic lights have been replaced with electronic LED based panels. These panels show different signs like arrows. So lets see what the future holds for us.