9004 and 9007 bulbs

These have two transverse (9004) or axial (9007) filaments in close proximity to each other. Is it possible to get both a very good low beam and a very good high beam at the same time in a single headlamp assembly from these designs?

Legally compliant, yes. Very good, no. Same goes for H13, H14, and a few similar designs seen only in the Japanese market. The high beam basically is a "copy" of the low beam, just shifted up and to the left (or up and to the right, in the case of headlamps for left traffic). It is not possible to optimize both beams, and it's very difficult to optimize even the low beam individually because of glare created by reflections off the nearby high beam filament.

H4 (HB2, 9003) doesn't have this problem, because the optics for it have separate zones dedicated to the low beam and to the high beam, but this bulb has a severe inefficiency on low beam because only about half the total reflector/lens area can be used to collect and focus light for the low beam, and it is a very old light source with a lot of potential for imprecise base-to-lamp fit compared to more modern designs. The new, forthcoming H19 is an efficiency improvement over the H4, but still has the old-type base.

-Virgil- said:

Legally compliant, yes. Very good, no. Same goes for H13, H14, and a few similar designs seen only in the Japanese market. The high beam basically is a "copy" of the low beam, just shifted up and to the left (or up and to the right, in the case of headlamps for left traffic). It is not possible to optimize both beams, and it's very difficult to optimize even the low beam individually because of glare created by reflections off the nearby high beam filament.

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Thanks for the explanation - it confirms what I suspected, but I thought I might have missed something.

I wonder what the impetus behind the design of these bulbs was - cost-cutting?

Do headlamp assemblies that utilize bulbs with transverse filaments typically have a shield in front of the filaments so that they can't be observed directly from the front?

jaycee88 said:

TI wonder what the impetus behind the design of these bulbs was - cost-cutting?

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Yes, low cost was a design goal of primary priority with the HB1 ("9004") and then the HB5 ("9007") and then the H13.

Do headlamp assemblies that utilize bulbs with transverse filaments typically have a shield in front of the filaments so that they can't be observed directly from the front?

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Some do and some don't.