Ok, now I get it.
You're talking about light intensity at given distance. Of course small lamps will still have lower output compared to more powerful ones, but it's exactly the spread of more lamps that makes the difference.
Used over a larger area, the same light emission allows plants to grow closer to the light, being useful in smaller grows and so on.
But there are limitations to be considered, regarding all light emission technologies. For example, 25W cfl bulbs have better lumen/W compared to higher(250) watt cfl(also less heat and electronic hazard), on the other hand a 1000W hps has higher lumen/W compared to lower W hps bulbs. Leds also need some minimum intensity to be considered useful, so there's plenty of factors to consider. Hard to say where's the optimum, some growers prefer narrow and more intense light for tall areas, some grow with fluoro tubes where plants touch the lights without damage.