1 . A century ago, kids were transported to school by all kinds of random vehicles. Because there were no national standards, it was up to states or individual school districts to hire buses, trucks and even horse-drawn wagons to convey kids to and from school.

Frank Cyr didn’t like this system. Back in the 1930s, Cyr was a professor at Teachers College, Columbia University, and an advocate for rural education. Cyr traveled the country conducting a study of school transportation. “In many cases, standards have been set up by more or less hit-and-miss methods,” reported Cyr in a New York Times article. He decided that something needed to be done to keep America’s schoolkids safe.

So in 1939, Cyr organized a conference in New York City dedicated to improving and standardizing the American school bus. He invited educators, transportation officials from 48 states and bus manufacturers to design a newer, safer school bus. At the meeting, Cyr hung up 50 paint samples on the walls of the conference room and formed a special committee to pick a winner. They chose the symbolic yellow-orange color that was originally known as “National School Bus Chrome”.

Cyr wasn’t a scientist or a safety expert, but he instinctively made the connection between bright colors, visibility and vehicle safety. “Based upon the standards of 1939, yellow was a very intelligent choice,” says Dr. Stephen Solomon, a retired optometrist (验光师) and founder of Visibility in Motion, which does consulting for emergency services providers. “The colors that are most easily seen by the human eye are the yellows — the yellow-green to yellow to greenish-yellow,” says Solomon. “That’s at the peak of the visibility range.”

Solomon explains that color vision is determined by photoreceptor cells in the retina (视网膜) called cones (视锥细胞). There are three types of cones, each tuned to detect different wavelengths of light: red, green and blue. Yellow light stimulates both the red and green cones at the same time, which is why the eye is most sensitive to colors in the yellow range.