Issues in the article:
...light output between 83 and 90 percent, however these did fail to meet certain requirements for light intensity and were found to be more likely to produce glare for oncoming traffic. Restoring headlights, while the most cost effective option, offered less of an improvement in light output than replacement. Professional and DIY restoration returned light output back to approximately 70 percent. Both restoration methods, however, produced more glare than is acceptable according DOT criteria.
So yeah, there's more light coming out the front of a new aftermarket headlamp versus a cloudy original, but the new aftermarket headlamps flunk even the super-lax performance requirements, both in terms of minimum allowable seeing light and maximum allowable glare. This is
not news.
And the word
aim doesn't appear even once in the whole article?! Inexcusable on its face, but it also screws up the rest of their "percentage improvement" claims, because as far as we know the lamp aim was random.
Issues in the research report:
"During testing, a re-aim of up to one half degree is permitted to improve performance relative to testing criteria" No, the allowance is for 0.25°, that is one quarter of a degree. Yes, it matters!
"Cutoff:European compliant headlamps have a very distinct cutoff line. U.S. compliant lamps have a more diffuse cutoff line that is intended to provide less distractive glare to oncoming traffic." No. The only purpose of the cutoff is to allow for visual/optical aim of the lamp. It is not designed, intended, or capable of reducing "distractive glare" (which isn't actually a term).
"New bulbs were used for both high beam and low beam operation in each individual headlamp" Whoah, big problem here. They used a different bulb for each individual headlamp? That completely invalidates their comparison. In real headlamp tests, an "accurate rated" bulb is used, that is a bulb that has been very carefully made and measured to be dead-nuts accurate in each and every item of the specification. This is done to eliminate the effects of bulb-to-bulb variability in service. For just one example, most bulb types have an output specification tolerance of +/- 15%, that is a 30% range of allowable intensity from the bulb. And then there are all the physical specs for dimension, placement, and orientation of the filament. There are allowable tolerances to account for the realities of mass production, but those tolerances must be factored out when comparing headlamps or the comparison's no damn good. Sheesh, this is a really super-basic screwup. They got access to a goniophotometer but didn't use accurate-rated bulbs...or even just use the
same bulb across all tests?! Unreal.
Quite a bit of random mess in the data charts. For example, on page 29 they have a compliance table for the Chevrolet Malibu high beam. Down at the bottom they seem to have added up all the candela values obtained at the various test points, to arrive at a total of 207,290.7 candela. What on earth they think this total represents is not clear; in fact it represents nothing. That's not how any of this works, you don't say "Well, this headlamp produces let's see here, 10 thousand over here, 20 thousand down there, 5 thousand here in the middle, 200 up there, so that's a total of...OK, this headlamp produces 35,200 candela". That doesn't mean anything, but the next few tables make it look like they're using it as the basis for comparing "how much light" the various aftermarket lamps put out compared to the genuine part. That's still not how any of this works. You can integrate
lumens in a beam pattern, but you can't add up candela values like this, because some of the individual-point values are higher and some are lower. I suppose you could use this total-it-up type of method if you were comparing the same lamp with various degrees of lens degradation (or dirt on the lens, or bulb age, etc). But across different lamps? No way!
"Aftermarket headlamps performed well, but did not comply with all test points. In particular, aftermarket headlamps did not meet FMVSS-108 specification for cutoff and failed to meet all requirements for intensity. Failure to meet specification for cutoff is interpreted to mean the headlamp is more likely to produce glare to oncoming and/or preceding traffic." That's probably true, and it also makes them difficult or impossible to aim correctly.
Not a single, solitary word about lamp aim, either, except to note that a laser was used to set up the lamps on the goniophotometer. Yes, that's standard practice, but it doesn't really translate to lamp aim on the vehicle...and all this talk in the article and report about DIY headlight replacement or having a shop do it, and the only mention of aim is at the end of the research report, as a buried mention that the dealer might charge to aim the lamps. Argh!
Don't get me wrong, the big-picture conclusion is absolutely correct: headlamp lens deterioration kills. That's not a secret or anything. Some years back one of the major OEM headlamp suppliers made a highly detailed presentation on that subject at the DVN Workshop in Detroit. I don't mean to seem like I'm trashing the whole report, but they sure shot themselves in the foot with some basic methodology screwups. If they hadn't, this report's conclusions would certainly be much more valid, much more fine-grained, much more realistic, and (perhaps most importantly) much more
usable to try to convince the regulators at NHTSA to do something about the problem (toughen up the regs).
LS400 said:
Seems odd that AAA would come out and declare their professional headlight restoration service
AAA doesn't offer a headlight restoration service. You can't bring your car to AAA and have them restore the headlights.