Wi-Fi uses radio waves to carry data between a device and an access point. Distance spreads the signal out, while objects can absorb, reflect or scatter some of its energy.

An invisible lamp is a useful first picture: placing a large obstacle in the way can weaken what reaches the other side. But radio also arrives along reflected paths. A house does not divide neatly into perfectly lit rooms and completely black shadows.

The useful question is where the connection changes and what else changed at the same time. Measurements test the picture; the picture cannot supply a room's speed.