The Science Behind Fire Engine Colour: Red vs Lime-Yellow

Why Are Fire Engines Red? The Science Behind Fire Truck Colors

When children are asked to draw a fire engine, they almost always paint it red. This choice seems natural since most fire engines are traditionally red. But have you ever wondered why fire engines are red? While the obvious answer might be that red stands out against most backgrounds, the real reason is more complex, involving how humans perceive colour.

How We See Colors: Day vs. Night

Our eyes perceive colours differently depending on the time of day. In daylight, our eyes are most sensitive to yellow-green colours, while at night, we’re more sensitive to green. This is because our eyes use different types of cells—cones during the day and rods at night. Rods are more effective at picking up light, particularly in the green spectrum. However, our eyes aren’t very sensitive to red, especially in the dark. Red can almost disappear at night!

Given this, if you want something to be visible both day and night—like a fire engine—a color like lime-yellow might be a better choice. This is why more fire trucks are being painted lime-yellow instead of red. Lime-yellow is also used for safety vests worn by workers, runners, and cyclists because it is highly visible.

Explore the science behind why certain colours are more visible at night

The Purkinje Shift: Why Colors Appear Different at Night

Spectral sensitivity refers to how well our eyes detect different colours of light. Our eyes have two types of receptors: rods and cones. Rods are better at detecting short wavelengths (like blue), while cones are more sensitive to longer wavelengths (like green and yellow). Cones work best during the day, with peak sensitivity at around 555 nm, while rods, used at night, are most sensitive to light just under 500 nm. This shift in sensitivity from day to night is known as the Purkinje Shift.

Due to the Purkinje Shift, red objects appear darker and are harder to see at night, while blue and green objects appear brighter. This phenomenon explains why some fire departments have opted for colours other than red for their vehicles—red fire trucks are harder to see at night. Conversely, red light is less likely to disturb our night vision, so car taillights are red. Red taillights are visible at night but don’t significantly interfere with our ability to see in the dark. In contrast, bright lights, such as white taillights or cell phone screens, can be very distracting in the dark because they make it harder for us to see well.

Does the Color of Fire Engines Matter? Research Says Yes

A study conducted in the 1980s in Dallas, Texas, found that lime-yellow fire trucks were involved in fewer visibility-related accidents than their red counterparts. While transitioning from red to lime-yellow fire trucks, researchers Stephen Solomon and James King observed that lime-yellow trucks were involved in fewer accidents where visibility was a factor. The study revealed that red pumpers responded to fire calls 153,348 times, while lime-yellow pumpers responded 135,035 times. Of 20 visibility-related accidents, 16 involved red pumpers, and only four involved lime-yellow pumpers. Moreover, when lime-yellow fire trucks were involved in accidents, the likelihood of injury or tow-away damage was significantly lower than with red fire engines (Solomon & King, 1995, 1997).

Despite this evidence, tradition is hard to break. While some organizations, like the Federal Aviation Administration (FAA), have adopted lime-green for their emergency vehicles, many cities continue to use the classic red.

The Impact of Color on Runway Safety

The runway holding position marking is red, but the blue taxiway lights at night present a “sea of blue” because they become brighter due to spectral sensitivity. The red lights used for stop bar lighting and taxiway markings for the runway ahead become duller and less noticeable than the blue lights. As a result, the probability of a runway incursion is higher at night.

Read more about the effects of colour on runway safety

Conclusion

The colour of fire engines and other emergency vehicles is more than just a matter of tradition. It significantly impacts visibility and safety, especially at night. While red has been the traditional colour, lime-yellow is a safer alternative, reducing the risk of accidents and improving visibility both day and night.

References:

• Solomon, S. S., & King, J. G. (1995). Influence of color on fire vehicle accidents. Journal of Safety Research, 26, 41-48.