Mirrors Reflect Green Best

If you've ever wondered what the "true" color of a mirror is, the surprising answer is a very faint green. A theoretically perfect mirror would reflect 100% of all light that hits it, making its color a pure, bright white. However, the common mirrors we use every day are not perfect. They are made from a sheet of glass with a reflective metallic coating, typically silver or aluminum. These metals are fantastic at bouncing back light, but they don't do so with perfect uniformity across the entire visible spectrum.

The science behind this green tint lies at the atomic level of the reflective coating. The specific structure of the atoms in silver or aluminum causes them to absorb a tiny fraction of light from the extreme red and blue ends of the spectrum. Consequently, they reflect light in the middle (Review) of the spectrum—around 510 nanometers, which our eyes perceive as green—with the highest efficiency. This difference is incredibly small in a single reflection, far too subtle for our eyes to notice when just looking at our own reflection.

This subtle bias becomes dramatically obvious, however, when you create a mirror tunnel. By placing two mirrors parallel to each other, you create a series of reflections that bounce back and forth. With each successive bounce, the mirror's slight preference for green light is compounded. The red and blue wavelengths are filtered out a little more each time, while the green light persists. As you look deeper into the "infinity" of reflections, you'll see them grow progressively dimmer and shift to a distinct, eerie green hue, revealing the mirror's hidden color.