Avoid running into another person when walking around a corner, thanks to this new and intuitive use of light and shadow!

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The Issue:

When a person is walking around a corner, there’s always a chance that they’ll unluckily collide with someone walking the opposite way (Figure 1).

Fig. 1: The person at left (yellow) and right (red) are about to collide at the “X”-marked location.

The fundamental problem is obvious enough: there’s just no way to see around the corner.

Hospitals and parking garages frequently solve this issue by placing a big convex mirror across from the corner, so people can see the reflection of anything approaching from the other side.

Unfortunately, it isn’t always feasible to place a mirror in the ideal location. It must be placed fairly far from the corner, and it must be OK to clutter up that space with a mirror and some sort of mirror-support post / arm.

Proposal:

Here’s a solution that will work whenever a mirror isn’t practical to install: just add two directional spotlights that will cast the shadows of anything going around the corner (Figure 2).

Fig. 2: Now these people probably won’t collide, since each of them will be forewarned by the other‘s shadow.


This won’t prevent high-speed collisions, but it should work fine at a typical walking or cart-pushing speed.


PROS: Possibly superior to the convex mirror solution: the human brain is likely to more easily recognize an approaching shadow as a danger (compared to a distorted reflection in a distant mirror).


CONS: Requires electrical power. Unlikely to work well outdoors during the daytime, since the spotlights will be almost invisible in bright sunlight.

Originally published 2026-06-15.