Light for Reading Priced Honestly: Why a Candle Cannot Serve a Schoolbook

Evening study is limited by illuminance at the page. Applying the inverse-square law, this paper computes the distance at which a candle, a kerosene lamp and a small LED lamp deliver 100 and 300 lux. The candle result is a disproof of the claim that a candle can serve for evening study: it reaches even the lower level only at a distance too close to a flame for safe, sustained reading. A modest LED lamp meets the higher level at a normal working distance. The physics, not the fuel price, decides this question. Computed results: candle_d_at_300lux_m = 0.058, candle_d_at_100lux_m = 0.1, kerosene_d_at_100lux_m = 0.173, led_lamp_d_at_300lux_m = 0.32, candle_lux_at_30cm = 11.1. Every number in this paper is produced by the accompanying script `compute.py`. SIMULATED, NOT MEASURED.