The shape that changed our world forever

TL;DR

Retro reflectors were invented by 3M to solve the visibility challenges of red stop signs, utilizing glass beads and cube retro reflectors to reflect light back to the source, making road signs highly visible even at odd angles and in low light conditions.

Transcript

did you know that stop signs used to be yellow back in the 1920s even though red had already become known for stop in traffic lights the convention in science wasn't yet established and there were two major problems with red one there wasn't yet a way to make red pigment that wouldn't fade and two red is way harder to see at night you see your eye ... Read More

Key Insights

• 🛑 Red was not initially used for stop signs due to visibility challenges, especially at night.
• 👾 Retro reflectors, invented by 3M, solve the visibility challenges of road signs.
• ⚡ Retro reflectors use glass beads and cube reflectors to bounce light back to the source, ensuring high visibility.
• 👾 Different refractive indices are used in retro reflectors to optimize visibility in both dry and wet conditions.
• 🙂 Road signs with retro reflectors are visible even in low light and at odd angles.
• 👾 Rain reduces visibility on road signs, but retro reflectors with varying refractive indices overcome this challenge.
• 👾 Retro reflectors are used not only on road signs but also on other surfaces such as plastics and clothing.

Questions & Answers

Q: Why were stop signs yellow in the 1920s?

Stop signs were yellow in the 1920s because the convention for using red as a symbol for stop in traffic lights hadn't been established yet.

Q: Why is red difficult to see at night?

Red is difficult to see at night because the human eye relies on rods, which are better at perceiving low light, and rods do not perceive red wavelengths. Only cones, which are less effective in low light, can detect red.

Q: How do retro reflectors work?

Retro reflectors work by using glass beads and cube retro reflectors to bounce light back to the source, ensuring visibility even at odd angles. The retro reflectors have different refractive indices for optimal performance in dry and wet conditions.

Q: How do retro reflectors overcome the challenges of visibility in the rain?

Retro reflectors have different refractive indices for dry and wet conditions. The elements with a refractive index of 1.9 work well in dry conditions, while elements with a refractive index of 2.4 work better in wet conditions. This ensures visibility of road signs even in the rain.

Summary & Key Takeaways

• Stop signs used to be yellow in the 1920s, but the switch to red happened due to visibility challenges.

• Red is difficult to see at night because it cannot be detected by rods, making it the most challenging color to perceive in low light conditions.

• 3M invented retro reflectors using glass beads and cube retro reflectors, which bounce light back to the source, ensuring highly visible road signs.