100 2600 lumen bulbs isn't just gonna give you 2600 lumens.... I'm sorry...
It may not stack as in double completely.. But if the light beams cross each other, don't tell me there's not more lumens in that spot.. I didn't know we have light experts here at riu...
And the distance from the bulbs at where the beams cross will determine the intensity... Or the lumens stacking.. Once again.. Sure they don't double or add exactly.. Your not rocking 260,000 lumens... And the cfl intensity isn't really high enough to get them close enough to add effectivly...
Sure 2 400's cover more since there is 2 light sources and you can put them apart from each other.... But if you put them inch's away under one hood.. The lumens will add where the beams cross.. Especially really close to the bulbs.. And in the middle of them.. I bet it's real close to stacking...
If someone wants to test this with a light meter and some lights they have.. I'd be glad to be proved wrong..
;o)