Rearview Mirror: The Day-Night TabControlling glare with a simple piece of wedge glass

From the show

Why it looks like that

Most manual rearview mirrors hide a clever piece of optical engineering inside the plastic housing. The glass is actually wedge-shaped rather than flat, offering two different reflection surfaces. Flipping the tab physically tilts this prism, swapping the bright reflection of the silvered back for the dim reflection of the front glass to reduce headlight glare.