Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux.
This is higher than the efficacy (of source) of most artificial lighting (including fluorescent), which means using sunlight for illumination heats up a room less than using most forms of artificial lighting.
Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98 000 lux (lumens per square meter) on a perpendicular surface at sea level.
The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky.
9Apps 4.9
