Daylight Amplification by Room Surfaces: How Much Light a Lime-Washed Ceiling and Walls Add, What It Costs per Lumen-Hour, and How Fast Kerosene Soot Takes It Away

Radiosity-lite (integrating-sphere) calculation for a 4.0 x 3.0 x 2.6 m room with a 0.8 m2 window (6,480 lm entering). Lime-washing walls and ceiling raises mean workplane daylight from 192.29 lux to 353.33 lux (+83.75%); walls alone give +45.06%, ceiling alone +12.91%. Maintained on a 6-month recoating cycle in a kerosene-burning household the time-averaged gain is +48.44% at $0.00468 per 1,000 added lumen-hours, 213.68 times cheaper per lumen-hour than kerosene light. Kerosene soot halves the gain in 3.73 months, against 20.49 months under clean light. SIMULATED, NOT MEASURED.