明るさのしきい値を設定する

An analog reading like 312 means nothing on its own. A threshold turns that number into a clear decision: dark or bright.

A threshold is a cutoff value. Readings on one side count as dark, and readings on the other count as bright.

Keep your cutoff in a named variable so it is easy to find and adjust later in one place.

Use an if statement to compare the live reading against your threshold and branch your logic from there.

Whether dark means a higher or lower number depends on how you wired the divider. Confirm it before you trust the test.

Print readings in a bright room and a dark one, then pick a midpoint between them as your starting threshold.

Pair your if with an else so the bright case is handled too, instead of doing nothing when light is high.

Near the line, tiny changes can flip the result back and forth. This rapid flicker looks like a glitch.

Hysteresis uses two cutoffs: one to switch on and a different one to switch off. The gap stops nervous flicker.

Feed the threshold from a potentiometer so anyone can dial in dark without re-uploading code.

This same threshold idea works for temperature, moisture, and distance. It is how sensors become decisions.

What problem does hysteresis solve at a light threshold?

You stored a threshold, compared readings with if and else, and added hysteresis so the decision stays steady.