Measurements of the illuminance
due to electric lighting were conducted when all blinds were
pulled all the way down to block out daylight with the dimming
controls disconnected. The illuminance given by the light fittings
was the difference between the illuminances with all lamp fittings
on and off. The working plane was taken at a height of 0.8 m above
the floor level. The room index was calculated to be 1.8 and over
160 measurement points were set.