I have somewhat poor night vision, so I put LED headlights in all my cars. But until now, I have not been entirely happy with them, until the new ones I found recently. The following pictures will explain things. This discussion deals with H4 bulbs only. They are used in the housings you can get to replace the sealed beam bulbs in a Fiero,, and they are also mused in my Ford Escape.
The picture below is a closeup of an H4 bulb. The two spring-like things are the filaments that light up when electricity is applied. The filament closer to the front of the bulb is the low beam light source, and the one closer to the base is the high beam light source. The little metal shield below the low beam filament ensures that it light goes only upward, where it strikes the surface of the bulb housing, and is reflected forward and downward to light the road but not blind oncoming cars. The result is a wide, flat beam. The high beam filament is allowed to shine in all directions so that it's light is reflected off all parts of the bulb housing. The result is a rounder beam that lights everything in front of you.
The picture below compares the H4 bulb to the kind of LED bulb I have been using. It has 4 LED elements, two that shine up for the low beam, and two that shine down for the high beam. The low beam elements are so large that the resulting beam is not nearly as precise as with the H4 bulb, with the result that sometimes oncoming cars flash their lights at me, because they think I have high beams on. When I turn high beams on, the bulb actually lights all four elements, since high beam needs light in all directions. But the low beam elements are not at the proper focal plane for high beam operation, and high beam just doesn't look "right'.
The below pictures shows the kind of LED bulbs I now have. These are BeamTech brand LED bulbs, and, as you can see, their LED elements are more closely positioned where the filaments are in the H4 bulb. Not only that, but there is a shield on each side to prevent the low beam element from shining downward. And in high beam, only the high beam elements light up, just like the high beam filament in the H4 bulb. The result is both low beam and high beam patterns that look correct. And there is another plus side of the BeamTech bulbs
The older style LED bulbs have a cooling fan on them. This is a potential source of trouble, and, in fact, the fan quit on one of the bulbs in my Ford Escape. The result was that the bulb would shine for a while, go out for a while, and repeat. Evidently the bulb has a thermal protection circuit that turns it off if it gets too hot, and back on when it cools down. The BeamTech bulbs only have a heat sink.
When I lived in Texas years ago, cars had to undergo an annual safety inspection. One of the tests involved shining your headlights into a gizmo to see of they were aimed correctly. I don't think the older style LED bulbs would have passed that test, but I'm sure the BeamTech bulbs would.
I drove my Escape some after dark tonight for the first time since replacing the bulbs, and i really like the patterns for both low and high beam. And no one flashed at me while I was in low beam.
