Lumen-Method Luminaire Count
How many fixtures to hit a target maintained footcandle level in a room, the IES lumen method: target x area / (lumens x CU x LLF), rounded up, with the achieved footcandles at that count. lux-to-footcandle does the forward illuminance from a known total.
Formula and source
count = ceil(target_fc x area / (lumens_per_lum x CU x LLF)); achieved_fc = count x lumens_per_lum x CU x LLF / area. 1 fc = 1 lumen per square foot.
IES lumen method (zonal-cavity number-of-luminaires relation, by name).
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