Examples of Illuminance

 
Summer, under a cloudless sky, in the open           100,000 Lux
Summer, under a cloudless sky, under a tree                 10,000 Lux
In the open, under a heavily overcast sky               5,000 Lux
Indoors by the window, shaded, clear day               2,000 Lux
Indoors away from the window                                  300 Lux
Full moon, in the open, on a clear night                  0.25 Lux
The target illuminance for an interior space depends on the specific visual tasks carried out in the space and can be anything from hundreds to thousands of Lux.
 
100 Lux                    interiors used occasionally with visual tasks confined to movement and for only                                limited perception of detail.
200 Lux                    interiors occupied for long periods, or for visual tasks requiring some perception of                       detail.
500 Lux                    moderately difficult visual tasks, perhaps involving colour judgement.
1000 Lux       very difficult visual tasks.
2000 Lux       exceptionally difficult visual tasks
(see CIBSE, Code for Interior Lighting for more details)