Modern headlamps: styling vs performance?

I find that most aerodynamic headlamps either sacrifice high beam performance for low beam performance in twin filament applications or sacrifice low beam performance for appearance in dual lamp applications. For the reflector type lamps it obviously follows that the larger the reflector and lens, the better you can distribute and focus the light your bulbs generates no matter how many lumens. The larger the lamp the less precise everything needs to be to get wonderful results, as they get smaller and smaller all the tolerances tighten up quick and sacrifices must be made. I'm fairly sure the engineers are not the ones saying, "Hey let's make a really poor lamp!" and they all go out for coffees. Projector lamps work differently but the same logic applies, the larger it is, the easier it is to get good results.

Small lamps are driven by smaller frontal area, reduced drag, fuel economy and the vagaries of style. I like to remind people, with a nod to Men In Black, that today's new hotness is tomorrow's old and busted. 7" round lamps were once The Standard but stylists came up with smaller sleeker front profiles and 5" rounds became popular. Round body shapes gave way to rectilinear shapes and suddenly rectangular lamps became popular, which then gave way to curvilinear and those little half height rectangular lights. And then enter the free form reflector aero lensed moulded plastic lamps of today. The freedom to say hey I'm going to make this very complicated curvature where the hood, grill and fender all merge with their wealth of character lines and bulges and flame styled hollows etc, and I'm going to make that the head lamp is amazing to a designer, not so much to the engineer. But believe you me, I do not want to drive a car styled by engineers any more than I want to drive the one engineered by the stylists. In a lot of these cases I've noticed that more lumens does not in fact yield better performance, a compromise lamp with a compromise bulb isn't going to get much better with more raw power.

ACAD_Cowboy said:

I find that most aerodynamic headlamps either sacrifice high beam performance for low beam performance in twin filament applications or sacrifice low beam performance for appearance in dual lamp applications.

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It's more complicated than that, but yes, low beam performance is generally prioritized over high beam performance. That's because most drivers use low beam most of the time. There are technical factors that go into it, too; with most two-filament light sources (HB1/9004, HB5/9007, H13, H14) the same optical surface must be used for both low and high beam, so both beams are compromised rather than optimized. With H4 you have an optical area that can be optimized for low beam and an area that can be optimized for high beam, but low beam efficiency is poor because you can only use about half the total reflector area to magnify and focus light on low beam. This necessitates a very large headlamp to get objectively good low beam performance. The new H19 gives better-than-H4 low beam efficiency while retaining the low beam and high beam dedicated optical areas.

As for high beam performance: the main constraint is the antiquated, very low ceiling on axial (straight ahead) high beam intensity in the US regulation, which allows only 75,000 candela. Depending on the type of lamp, the UN regulations the rest of the world uses permit double to triple that intensity. In general, low beam performance has been increasing over the years and decades, to the point where the peak intensity in today's good low beams are approaching the levels that we've seen from decent high beams for a long time. From the driver's perspective, the apparent change in intensity when switching from low to high beam is often nowhere near as visually stark as it used to be.

For the reflector type lamps it obviously follows that the larger the reflector and lens, the better you can distribute and focus the light your bulbs generates no matter how many lumens.

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That is true.

The larger the lamp the less precise everything needs to be to get wonderful results

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That is not necessarily true.

Projector lamps work differently but the same logic applies, the larger it is, the easier it is to get good results.

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Also not necessarily true.

In a lot of these cases I've noticed that more lumens does not in fact yield better performance

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It's not clear what lumens you're talking about here. Lumens off the light source (bulb)? Lumens in the beam (on the road)? More lumens off the bulb doesn't necessarily mean a better headlight beam. More lumens in the beam -- as long as those lumens are being distributed usefully -- does mean a better headlight beam.

a compromise lamp with a compromise bulb isn't going to get much better with more raw power.

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That's true, a poor headlamp does not really become a good headlamp with a brighter bulb. That said, a better bulb can compensate, to some degree, for inherent inefficiencies in a headlamp. See here for some interesting, data-based examples.

My Seat Leon has LED headlights, but they don't seem any improvement ( as far as lighting up the road ) to the xenon ones in my previous car.

Maybe other benefits I don't know about ?

Maybe I should go for a vn upgrade ?

billabong said:

My Seat Leon has LED headlights, but they don't seem any improvement ( as far as lighting up the road ) to the xenon ones in my previous car.

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They probably aren't -- there is no technical, regulatory, or logical reason why they should be (in fact, the Xenons in your previous car might well have given better performance). But the LEDs in your Leon consume less power and have longer lifespan.

-Virgil- said:

They probably aren't -- there is no technical, regulatory, or logical reason why they should be (in fact, the Xenons in your previous car might well have given better performance). But the LEDs in your Leon consume less power and have longer lifespan.

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I wonder if anyone has numbers for these ? Make, output, etc

ACAD_Cowboy said:

I find that most aerodynamic headlamps either sacrifice high beam performance for low beam performance in twin filament applications or sacrifice low beam performance for appearance in dual lamp applications.

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Sacrifices are made, but low beam performance usually (usually) is not what gets sacrificed. Low beams are used most (either through necessity/legality, but also through driver error, since there are many drivers who think their low beam performance is so good they don't *need* high beams).

For the reflector type lamps it obviously follows that the larger the reflector and lens, the better you can distribute and focus the light your bulbs generates no matter how many lumens.

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Very much so.

The larger the lamp the less precise everything needs to be to get wonderful results, as they get smaller and smaller all the tolerances tighten up quick and sacrifices must be made.

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A sloppily built large lamp will not necessarily outperform a well-built smaller lamp, though. Tolerances are still critical, from the filament placement in the bulb to the rest of the reflector.

I'm fairly sure the engineers are not the ones saying, "Hey let's make a really poor lamp!" and they all go out for coffees.

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They're the ones told "make a lamp fit in THIS package" and then watch the marketers who told them that go out for coffee.