Actually, I wouldn't think.

1) "brightness" is a very subjective thing. Doubling the number of lumens or lux doesn't make the light seem "twice as bright", and

2) just because the light uses twice as much power, that doesn't mean it emits twice as much light -- it also matter how efficient that particular emitter is at that particular power level, and there's a lot of variation there. It's entirely possible that the one watt light emits less light than the half watt light. Our four times as much.

Really, "watts" is a really poor indicator of how good a LED light is -- if you must pick just one number to describe a complicated thing, lumens emitted would be the number to pick, but of course the beam pattern factors into how good it is too. (The beam pattern needs to be what you need it to be for your particular application.)