Daily or during-attack exposure to a narrow slice of dim green light. Small studies report less light pain, milder attacks, fewer headache days, and better function; a systematic review judged that evidence as very weak. Brighter or mixed-color light can worsen pain and light sensitivity. Add-on with little whole-body risk; benefit remains uncertain; research is financially entangled with the products. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Monthly headache days | ≥50% reduction from own baseline | Primary endpoint in the 2021 crossover |
| HIT-6 score | ≥6-point drop; functional target often <50 | Captures disability, not just day counts |
| Pain intensity (0–10 numeric rating) | Drop of ≥2 points or ≥30% from baseline | Secondary in 2021 |
| Photophobia rating (0–10 during a standard indoor light) | Stable or falling versus baseline; a rise during a green session is a stop-rule | Directly tracks the High-level harm |
Cadence: 4-week baseline diary, HIT-6, and 0–10 pain before first session; repeat at 2 weeks, 4 weeks, and 10 weeks, then every 3 months if daily use continues