Posted By Ken Taylor
There are various pieces of guidance and standards around. The Regs require lighting to be suitable and sufficient and point us to HSG38 (now revised) and to the CIBSE publications (which are expensive). I consider the 300-500 lux mentioned to be a reasonable guide for many general offices with computers these days. 300 lux is the minimum standard for school classrooms and computer users are said to tend to need something like this whereas printed paper reading may require something nearer 500 and fine detail work will need more.

Posted By Marcus Pereira
I had the same query - after lots of internet time I found this... sorry I cannot remember the source of the info.

Typical Average Maintained Illuminance Values
Typical recommended average maintained illuminances for general lighting are:
For offices: 500 lux, or between 300 and 500 lux for offices with Visual Display Screens (e.g. computer screens). The actual value depends upon the extent of use of display screens; if personnel are viewing screens continuously, or nearly continuously - 300 lux.
For manufacturing areas: Usually 300 or 500 lux depending upon the difficulty of the visual task. Can be higher for visual tasks with very small detail/low contrast.
Retail stores: General lighting objectives range from 150 lux for specialised retailers that use a lot of display lighting to 1000 lux or even higher for supermarkets that use very little if any display lighting.
A comprehensive schedule of recommended maintained illuminances is included in the CIBSE Code for interior lighting.