Colour temperature is a totally different thing to light output. You're talking solely about light temperature. Playing with the chemistry of the filament and the envelope filler gas can change the proportions of Heat and Light produced by a given current flow through the bulb. I don't know how in detail; my materials science is about 27 years old.

Exactly. That's why SAD lamps are so common now and why the old warm white are not so common, it's a whiter more effective lamp for a given situation. As we both agree, 55W is 55W in any language.

New bulbs fitted and headlights adjusted up a little bit (by my friendly local MOT station), there is a noticeable improvement (both from the bulbs and from the adjustment) but fairly sure the octy headlights are still not as good as other cars I've had.

They are absolutely shocking, I might get mine adjusted. I can only see about 10-12 feet in front of me with dipped beam its damn right dangerous :(

Exactly. That's why SAD lamps are so common now and why the old warm white are not so common, it's a whiter more effective lamp for a given situation. As we both agree, 55W is 55W in any language.

55W is the input power; it's not the output light level.

Let's say that the reference lamp dissipates 55W of electrical power, producing 50W of heat and 10 lumens of light.

My new "100% brighter" lamp dissipates the same power, but due to changes in filament design and filler gas chemistry, produces 45W of heat, and 20 lumens. Do you see the point now?