Stop Red: Why Is 'Red' the Color for Danger?

All light travels in waves, but different colors have different lengths. Red light has the longest waves in the visible spectrum. Because these waves are so long and 'lazy,' they are very good at stepping over tiny obstacles in the air like molecules of nitrogen or oxygen without getting knocked off course.

When the air is full of fog, rain, or dust, short waves like blue and green crash into the particles and scatter everywhere. Red light, however, can 'punch through' the gloom. This makes it visible from a much further distance than any other color, which is vital for safety.

Humans have also evolved to pay attention to red. It is the color of fire and blood, which naturally tells our brains to be alert. By using a color that travels well through bad weather and naturally grabs our attention, engineers created a stop signal that is very hard to miss.