I Traced the History of the Traffic Light. It Began 35 Million Years Ago

Quick Overview

The selection of red and green for traffic lights, which seems counterintuitive based on human color perception, is actually rooted in physics, biology, and railroad history, ensuring red's superior visibility in adverse conditions due to its longer wavelength and less scattering, while the historical development of traffic signaling involved early gas-lit semaphore systems that eventually led to the standardized three-color electric light system we use today.

Key Points: Red light was chosen for stop signals because it possesses the longest wavelength in the visible spectrum, resulting in less scattering by atmospheric particles like fog and rain, maximizing visibility. The color red is biologically associated with danger, anger, and arousal in humans, making it an ideal, universally recognized warning signal. Early traffic control systems involved manual signaling using flags or colored glass lamps, such as the gas-lit semaphore invented by John Peake Knight in 1868 in London. The first electric traffic light, invented by Lester Farnsworth Wire in 1912, used red and green bulbs, which caused confusion when drivers with color blindness could not distinguish between them. William Potts, a Detroit police officer, is credited with inventing the four-way, three-color traffic signal in 1920, adding the crucial yellow light to signal caution. Primate color vision, particularly in species originating outside Africa, often involves only two color-sensitive cones, making distinguishing between red and green difficult, which is why the visible spectrum's red and green wavelengths are so distinct for human vision. The prevalence of red as a danger signal across nature (poisonous animals) and culture (warning signs) reinforces its instinctive use for stopping.

Context: This video explores the historical, physical, and biological reasons behind the choice of red, yellow, and green for modern traffic lights, addressing the common misconception that these colors were chosen purely for scientific reasons. The narrative traces the evolution from early railroad signaling using semaphore arms and colored glass, through early electric prototypes that caused confusion due to only having red and green, to the standardized three-color system introduced in the 1920s, linking these conventions to physics (Rayleigh scattering) and human biology (trichromatic vision).