Lumens, schmumens. This is silly-talk.
Yeah, in terms of light intensity measured at the SOURCE, two, ten or one hundred 26 watt bulbs next aren't any brighter than one. But SO WHAT? That's really NOT what's important to growing.
What matters isn't the intensity of the light measured at its source. If you're trying to grow plants what matters is the total quantity of photosynthetically useful light hitting your plant(s).
If you've got ten 26 watt CFL bulbs then you're putting out ten times the total amount of light, and ten times the total amount of light energy, as one bulb. If stick a plant under your ten bulbs, it will be hit by ten times as many photons as one put under one bulb, and grow that much better.
So OF COURSE ten bulbs are going to massively outperform one bulb. This is so blindingly obvious to anyone who has actually tried to cultivate plants under artificial light, its frankly embarrassing to have to point it out here.
I mean if there is no difference between one bulb and twenty bulbs, then why do commercial growers fill gigantic warehouses full of 1000W HPS bulbs? Hell, why even use 1000W lights at all? Do these people. . .who make their living growing plants. . .NOT know what they are doing? If it doesn't matter if you have 1 bulb or 10,000 bulbs, why can't you grow 10 foot "trees" under one 26W CFL bulb?