How many square meters of office area can a 40-watt fluorescent lamp illuminate?

The illuminated area of ??the lamp.

First of all, it depends on what you call "brightness", that is, how much "illumination" (the number of lumens in 1 square meter) is required. Office illumination ranges from a low of 150 to a high of 300 lumens/square meter, and some require more than 500 lumens/square meter.

Again, it depends on the size of your room and the color of the walls, that is, how much light the walls can emit. For example, if one light is used in a 20 square meter room, then the same three lights will be darker in a 60 square meter room, because the wall area is not three times larger and there is less reflection.

It also depends on how high the lamp is hung.

Based on the general office estimate, a 40-watt fluorescent lamp can illuminate an office of about 20 square meters.