Low-beam headlight dark spots

[pbierre]

I bought my 2004 XC70 a few months back, and recently drove from SF Bay Area to San Diego with much night driving.
The low-beams are not throwing a good illumination pattern. Rather, there are semi-circular occlusions (dark spots) right where the beam should be brightest (see photo).

The high beams present two well-shaped cones that overlap and project at the correct angle, so I don't think the answer involves
the headlamp assy. steering knobs -- that would put the high-beams out of alignment.

Any ideas how to go about fixing the low-beam pattern?

[hoonk]

Glass or plastic headlamp lenses? Either way I have seen many incorrectly installed H7s or H11s. (upside down, clipped only on one side, jammed at an angle, not secured at all) I would guess the left bulb is not seated correctly. The pattern on the left one is low also, but that may be corrected by installing the bulb properly.

[Allgonquin]

2004 should have glass lenses, at least mine does. However mine has the situation where the driver side headlight bulb mount is messed up. The bulb mount inside the light fixture in this case. I can not mount the bulb properly so the pattern is skewed and irregular. I don't know whether this issue is particular to my car or whether it's a "thing" with this model year.

[pbierre]

I think I got to the bottom of this problem. The left side had the biggest dark spot, so I examined the bulb from the external (polycarbonate lens) of the headlamp assy with a flashlight. The obscuration cylinder was bent noticeably downward....it is supposed to be co-axial with the bulb. The optical design theory-of-operation is that the bulb filament is supposed to serve as a point source of bright light shooting back against the reflector, so all the light thrown is indirect. The bulb itself has an opaque
endcap so that the filament cannot sting the eyes of oncoming drivers. The obscuration tube is there to prevent looking directly at the bright filament from an angle. My guess is that its inner surface acts as a reflector, and thus it is an optical component that must be approximately aligned with the axis of the bulb.

I removed the round plastic weather cover, pulled off the wire harness, undid the spring clip retainer (pull it sideways at the top, then outward). The bulb then lifts out. Try to remember its orientation -- there is a tab on the collar for alignment.

Yes, if you fail to properly seat the bulb (tab matched up with notch), then the bulb filament will be off-axis, and that will skew the
light pattern thrown onto the road.

To straighten the obscuration cylinder, I just stuck a finger in the hole and bent it upward. Then, reassembled everything.

The "after" photo was taken at dusk, and shows the desired wide pattern for the low-beams. The road in front now looks much better when driving at night.

[Xfingers]

Congrats on sorting your problem and thanks for the in-depth explanation on how these lights are designed to work.