Garmin Varia RTL516

You won't want to be without the Varia RTL516 after a short time: Before you hear the cars, you already have them on your screen. However, at 108 grammes, it is heavy and not exactly cheap.

... The light itself is not overly bright, but it is amplified via a lens. The intensity can be controlled via the bike computer. There is also an automatic mode in which the rear light adjusts its brightness to the ambient light. There is a small red light in each side to ensure visibility across the direction of travel.