Light Output

I have setup two Phillips ColorTone F40C50 40W Fluorescents above my work
area, at a distance of approximately 36 inches -- I know that's not a huge
distance. I have measured the illuminance on my work area to be 400 Lux. If
I want the illuminance to reach 2000 Lux on my work area what course of
acton would you recommend: add more of the same lamps or switch to higher
Lumen lamps?

Regards,

Roger Breton