Evening Study Light as a System: Panel, Battery and Lamp Sized for Three Hours at Reading Illuminance

Evening study light is a small system, not a lamp alone. This paper sizes panel and battery around a stated 3 watt LED lamp used three hours per evening, with two evenings of reserve, and prices the whole system. It complements the illuminance bound for single flames: here the question is not whether the light suffices at the page, but what the reliable supply of that light costs per household. Computed results: nightly_Wh = 9, battery_Wh = 21.2, panel_W = 2.7, system_cost_usd = 37.08. Every number in this paper is produced by the accompanying script `compute.py`. SIMULATED, NOT MEASURED.