How daylight calculator Works
Usable vs official light
Sunset time is an astronomy fact; usable light is a terrain fact. Forests and canyons lose readable trail 30–60 minutes before the calendar sunset, east-facing slopes lose it earlier still. Planning against the official number in a canyon is how "we had an hour left" becomes headlamp descent on scree.
The 70% rule
Hike plans that fill 70% of the daylight window leave a 30% buffer for the real things — route-finding, blowdowns, swim stops, a turned ankle. Plans at 90%+ of daylight are not ambitious; they are headlamp descents with extra steps. The season select prices winter's early dark honestly.
Night hiking as a plan, not an accident
Deliberate night hiking (alpine starts, full-moon ridge walks) is legitimate and wonderful — with real headlamps, spare batteries, and practiced navigation. The failure mode is unplanned night hiking: the same terrain, no practice, dying batteries. One is an adventure; the other is a callout.