Place the mirror in front of the black background.
Look at the mirror in such a way that you can only see black on it.
Shine the flashlight on the mirror from the side, perpendicular to the direction of your gaze, without illuminating the black background.
Observation:
The background around the mirror is brightly illuminated, while the mirror remains black.
Tip:
The effect is particularly good when the background is white and the room is darkened slightly.
Explication:
The light that falls on the mirror is reflected in a direction where the observer’s eye is not. If the background is black, the mirror will also appear black. The environment of the mirror, on the other hand, reflects the light diffusely, i.e. it scatters it in all directions, including that of the observer’s eye. That’s why the surroundings appeared brightly lit.
