Why Japan calls a green traffic light blue (青)

In Japan, the green traffic light is called 青 (ao), blue: it’s the 青信号 (aoshingou), the “blue signal”. This isn’t a mistake. The Japanese word ao has long covered both blue and green, and that older meaning still lives on in traffic lights, fresh leaves, green apples and green onions.

What the kanji says

青 has two parts. The top, 龶, is a squashed form of 生, growing plants. The bottom looks like 月, the moon, but has nothing to do with it. The traditional reading is 丹, cinnabar, a red mineral used for dyes, which came to stand for colour; some scholars see 井, a well, there for its sound instead. The usual explanation is that together they mean the colour of growing plants, a blue-green.

So even the kanji is a little green: it’s the colour of new leaves.

Why the green light is blue

The Japanese word for green, 緑 (midori), is thought to have first meant fresh shoots and buds, and only later become a colour. For a long time, ao stretched over both blues and greens, which is why 青葉 (aoba), fresh leaves, 青りんご (aoringo), green apples, and 青ねぎ (aonegi), green spring onions, are still “blue” today. Like several colour kanji, such as 紅 (beni), crimson, and 紫 (murasaki), purple, 緑 has 糸, silk thread, in it; its right side gives the sound.

Japan’s first electric traffic lights went up in Tokyo in 1930, and before the war the official name for the colour was 緑, green. Newspapers called it 青 anyway, the name stuck, and in 1947 the law itself switched to 青信号. Then, in the early 1970s, the National Police Agency asked for the lights to be made as blue as possible while still counting as green under international standards. So Japan’s “blue” lights really are a bluish green.

And black

The video gives 黒 (kuro), black, a story too: the four dots at the bottom, 灬, are flames, and black is the colour of soot. That’s the traditional explanation, from the Shuowen Jiezi, a Chinese dictionary from around 100 CE, which reads 黒 as a chimney over a fire.

Many modern scholars read the oldest forms differently: a person with a tattooed face, the mark once used to punish criminals in ancient China. In this view, writers later reinterpreted the shape as fire under a chimney, and the bottom was redrawn to look like flames. Either way, fire and soot make 黒 easy to remember. The tattoo punishment itself was called 墨 (sumi), ink, the kanji you’ll still find in 入れ墨 (irezumi), a tattoo.

How to use it

• 信号が青になったら渡ろうね。

  Shingou ga ao ni nattara watarou ne.

  Let's cross when the light turns green.

• 今日は空が青いね。

  Kyou wa sora ga aoi ne.

  The sky's so blue today.

• 顔が真っ青だよ。大丈夫？

  Kao ga massao da yo. Daijoubu?

  You've gone white as a sheet. Are you OK?

• 青ねぎを多めにお願いします。

  Aonegi o oome ni onegai shimasu.

  Extra green onions, please.

• Today, 青 mostly means blue. For a green car or a green shirt, say 緑 (midori). The green meaning survives in set words: traffic lights, 青葉, 青りんご, 青ねぎ, and 青菜 (aona), leafy greens.
• The full set of lights is 赤信号 (akashingou), red, 黄信号 (kishingou), yellow, and 青信号 (aoshingou), green.
• 青い can also mean pale: 顔が青い (kao ga aoi) is “you look pale”, and 真っ青 (massao) is either deep blue or deathly pale.
• And young: 青い can mean unripe or inexperienced, and 青春 (seishun), youth, is literally “blue spring”.

Words with the same kanji

Remember it

Green shoots (生) on top, a pot of pigment (丹) below: 青 is the colour of growing plants. That’s why a traffic light can be 青 and still be green.

The kanji in this lesson

Tap Draw it to watch the stroke order. Numbers show where each stroke starts.

Draw it

Draw it

Draw it

Sources

• Wiktionary: 青
• Kuruma News: why the green light is called 青信号 (in Japanese)
• Wiktionary: 黑 (the origin of 黒)
• Kotobank: 緑 (デジタル大辞泉 and 世界大百科事典)
• Wikipedia (Japanese): 信号機 (the pre-war name 緑信号)

Written by the Chirami team with the help of AI, then checked against JMdict and KANJIDIC2. How we write lessons. Spotted a mistake? Email support@brightsmilesolutions.org.