First, I personally prefer the term 'e-code' for the older substitutes for sealed beams, and the term 'euroheadlight' for the very specific or proprietary (non-generic) lamps of auto manufacturers for their particular model cars, such as a later Volvo 240 -- but I won't force that on anyone who disagrees.

In any case, what makes an e-code or Euroheadlight different from those headlights in older U.S. cars is a combination of attributes. First, such european market lamps must have certain beam patterns, particularly with their low beams. There must be a sharp cutoff so as to prevent light from hitting the eyes of oncoming drivers. There must also be a somewhat higher cutoff on the other side of the road, to enable the driver to see farther and notice hazards at a greater distance. In some lamps, such as the Cibie-Volvo genuine european headlights, that cutoff rises at about 15 degrees from the horizontal, so that at the side of the road, the illumination is high enough to light up road signs and eyeshine of deer. Note that this is why you can't use lamps from the U.K., because they drive on the "wrong" (ha, ha) side of the road, and the cutoff is reversed. But the improvement in night vision in low beam is startling, and the reason why I cannot tolerate anything else (note my earlier message about my "old man's eyes").

Of course, there are other features, as well. I strongly suggest getting a copy of the Bosch Automotive Handbook -- it's worth its weight in gold as far as the information it contains, not only on lighting but on almost all aspects of automotive engineering.

Anyway, in contrast to the european headlights, during the era when our later ('85-on) 240's were imported, our stupid gov't's DOT deemed that those european headlights were prone to glare (although quite the opposite, really) and dictated a beam pattern that directed most of the light from our headlights down on the pavement just a few feet in front of the car. Thus, with OEM (U.S.-market) plastic headlights, we drive on low-beam with just a bare fringe of light shining ahead to light our way.

The differences are all about the design of the reflectors and the front lenses. You can't just put brighter filaments in those lousy headlights -- you'll still be wasting the photons being produced. You need altogether different optical design. Read the Bosch book, and you'll understand it.

Good luck.