An evaluation of classroom-illumination: A critical requirement for effective designing and construction of naturally-illuminated schools in Nigeria

Indoor lighting-levels (illuminances) of 180 classrooms in 60 public [primary and secondary] schools located in all six geopolitical zones of Nigeria, were experimentally investigated 12 times under three different sky-conditions ['clear', 'partly-clear' and 'overcast'] using the Hagner digital lux-meter. The analysed empirical-data were: 'Mean indoor illuminance for tasks on desks' tops near windows exposed to direct sunlight and/or higher illumination(Ld(DSL) )' ranging from 1,243 lux-4,486 lux, 'Mean indoor illuminance for tasks on desks' tops near windows exposed to indirect sunlight and/or lower ( ) illumination( )' Ld ISL ranging from 674 lux-2,987 lux, 'Mean indoor illuminance for tasks on desks' tops at Center of ( ) Classroom( )' Ld CrC ranging from 101 lux-449 lux and 'Mean indoor illuminance for tasks on boards(Lb)' ranging from 110 lux-494 lux. Three globally recommended standards' ['CIE-ISO', 'IESNA', and 'EN'], values [of minimal/optimal lighting-levels for classroom-activities like 'reading on the blackboard' ( s Lb 500 lux) and 'writing, drawing and reading on desks' ( s Ld = 300 lux)]; and the follow-up statistical-analyses reveal 'excessive solar irradiation' and/or 'inadequate illumination' in the classrooms. © 2019 Inderscience Enterprises Ltd.