A public school law requires a minimum illumination of

Question

A public school law requires a minimum illumination of 165 lx on the surface of each student's desk. An architect's specifications call for classroom lights to be located 1.6 m above the desks. What is the minimum luminous flux the lights must deliver?

_____lm

Answer 1

the illumination in ft-c varies inversely as the square of the distance from the source

ft-c = Lum / (d ^ 2)

conversion

d = (1.6)(3.28) = 5.248 ft

ft-c = (165) / (10.764) = 15.33 ft-c   school requirement

Lum = lumen output of lamp

Lum = (15.33)(5.248) ^ 2

Lum = 422.21 lumens

remarks: the requirement of 15 ft-c on task is low. according to IES Lighting Handbook

library study and notes 70 Ft-c

library ordinary reading 30 ft-c

school reading printed material 30 ft-c

school reading pencil writing 70 ft-c