A lumen rating is useless without context. A lumen is defined in terms of distance; it's the metric equivalent of foot candles. How many individual candles worth of light do we see at X distance. (A candle is basically defined to be the amount of light needed to read a paragraph of newspaper print )
The only real way to compare lights is using lux; the measurement of square meter lumens. Think of this as a newspaper unfolded all the way out. You'd be able to read the whole page with 1 lux of light.
So for example, the Light Force 35w HIDs I run... they're rated as being 1 lux @ 800m. The 50w versions are rated as 1 lux @ 1100m.
I wish more companies would state their ratings in the same way, and actually give the distances their lumen ratings were taken at. Unfortunately they will often state lumens as being read about an inch off the bulb. Not very useful, and it totally ignores reflector design. Or they'll measure at where the bulb+reflector yeilds the best lumen rating, but not tell you where that was... it could have been a foot away, or a mile.