This uses flickering light seen through closed eyelids — a way to nudge hypnagogic imagery and prime lucid awareness. Red carries through the lids best.
Read first: flashing light can trigger seizures in people with photosensitive epilepsy. Don't use it if that applies to you, or if you're driving or operating anything. The rate is capped in the calmer 1–13 Hz range, but stop if you feel any discomfort, nausea, or twitching.
Set your phone brightness to max, lay it face-up beside your pillow, close your eyes, and keep a soft intention in mind. Tap the screen during a session to show controls.