Turn the shutters.
Let the garden glow.

Every shutter changes the signal.

A bright shutter dot flips the incoming lamp: on becomes off, off becomes on. A dim dot leaves it alone. This is XOR: two lights cancel.

The small arrow turns the incoming signal.

It happens before that row's shutter. Shift a shutter left or right; its last dot wraps around. Match every marked reading, including the bottom receiver.

There is time to experiment.

Select a row, then use ← / → or the on-screen buttons. ↑ / ↓ selects another row. Undo, redo and exact-search hints are always available. No timers, no penalty for thinking.