Night Navigation Calculator

Headlamp runtime is modeled from basic LED electrical draw: power consumption is estimated as lumens divided by 80 (a typical LED efficiency figure), and runtime on high mode comes from standard battery math — capacity in mAh times voltage (3.7V, standard for lithium cells), divided by that power draw. But racers rarely run on high mode the whole night, so the calculator splits your night hours into moving and stationary time based on your input percentage, then assumes you'll run high mode for about 60% of moving time, a dimmer low mode the rest of the time and half your stationary time, and the lamp off for the remaining stationary time. Low mode is modeled as drawing only about 30% as much power as high mode, so the "effective burn hours" figure — and the resulting number of battery sets and spare batteries you'll need — accounts for that mixed usage rather than assuming worst-case full brightness all night. Battery weight assumes standard 18650 lithium cells at about 48 grams each.

Beyond battery logistics, the calculator estimates how much darkness slows you down: a 30% baseline speed penalty at night, increased for rougher terrain and reduced somewhat if your headlamp is bright enough (500+ lumens) or increased if it's dim (under 200 lumens). It also recommends a minimum brightness tier based on your selected terrain difficulty — from 150 lumens for road/path up to 800 for technical scrambling — and reports how your actual headlamp compares as a lumen-adequacy percentage. If your lamp falls short of the recommended tier for your terrain, expect the night speed penalty to run higher than shown, since the model assumes adequate lighting for the terrain type selected.