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Sealed beams and comparably-sized E-code units tend to put out about the same total amount of light, but it's directed differently. The sealed beams put out an intense "hot spot" shifted slightly downward and rightward (on low beam) with very little light on the road surface ("foreground light"), narrow spread and a relatively high amount of light directed upwards (which US regulators claim is vital for seeing overhead road signs and is also terrific for blinding you in bad weather with backdazzle) ECE headlamps with H4 bulbs tend to have lower peak ("hot spot" intensities, sometimes MUCH lower (50%!) but the beam is wider, there's a lot more foreground light, and there's an upsweep to the right that does a good job with shoulder-mounted road signs as well as 2- and 4-legged critters about to step into the road. So the ECE beam is better formed, but with a relative weakness in strength of distance-vision light with traditional H4 bulbs in small lamp sizes, while the sealed beam produces a poorly-formed beam with lots of distance-vision light and not much of anything else. In addition to total output, the location of the hot spot is very important. The farther away from "straight ahead" it is in both the downward and rightward directions, the shorter your seeing distance. The best mix is lots of down-the-road light WITH good foreground light, WITH good spread, WITH a sharp cutoff and good control of upward stray light. Foreground light merits additional discussion: There's definitely such a thing as too much. This is why putting overwattage bulbs in E-code headlamps to boost the down-the-road light does not necessarily make the beam pattern better overall. For one thing, the location of the hot spot doesn't change -- if it's way over to the right, it's going to stay way over to the right. Also, the ratio of foreground to distance light stays the same, but the absolute level of foreground light is higher. Your eyes' pupils constrict in response to the flooded foreground -- this cuts your distance vision. That's why the beam pattern is more important than the overall amount of light (putting a theoretical 500W bulb in a headlamp producing a bad beam pattern wouldnot make it produce a good beam pattern...) The difficulty with H4 in a small reflector is that the H4 bulb uses a spoon-shaped shield under the low beam filament to create the low beam cutoff. It does this by blocking off the lower 40% of the reflector from view of the low beam filament. Bam, 40% less reflector area. This is less of a problem with large reflectors, but a serious problem with small ones. Newer technologies that don't rely on a physical blockoff shield to create the cutoff give us good beam formation (wide, foreground, distance, minimal upward stray, etc.) *with* use of the whole reflector. Example:
The Hella example above is picked because we were discussing 'em recently. Other H4 lamps produce vastly different results -- I have lab tests of five or six different 7" round H4 E-code headlamps with hot spot intensities ranging from 11,400 to 24,400 and locations ranging from 4.2R/2.2D to 0.9R/0.7D, with the same bulb in the same tester in the same lab. They are NOT all the same. Finally, foreground light is like a security blanket: It causes us to subjectively judge headlamps "good" when in fact they offer relatively little distance vision. Unfortunately, the human eye is a notioriously poor judge of character in headlamps -- we know what we like and what we don't, but our likes and dislikes don't accurately match our safety needs. We need more foreground light than cruddy US lamps offer, but we need more distance light than cruddy ECE lamps offer.
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