Why the red light is used as a danger signal?

Why do people whose native language is not English, always ask retarded questions??

This is Maintenance and Repairs category, not automotive history.

colour of blood - as in you cut / hurt yourself = danger

It is the color most easily seen.

No real reason for it other than tradition. It could be blue or green or any other color, but in OUR culture, red has been used as a warning symbol for thousands of years. Maybe it has something to do with red blood.

Because people like you have no clue when things get dangerous!

I've looked into this before and the oldest use I found was in rail travel, with the red lights on cabooses. Rail cars were the descendants of mining carts and I haven't found anything about lighting on mining carts. That makes me think the basic rail lighting of a white light on the front for vision and and red light on the rear for warning was chosen for practical reasons - they must have been gas powered in the 1800s. Yellow would be more penetrating but could be mistaken for white.

it's an ancient tradition red is blood and spells danger it's quite obvious really