Mark,

I use DRL since day 1, and in 1.5 years I've had the car, I only replaced 1 headlight bulb.

A couple of months ago I purchased a set of great Philips VisionPlus bulbs - Philips is one of Volvo's OEM partner companies, and these bulbs had been recommended by Arno. I had no other option but to try them. What great bulbs they are! Definitely much brighter. [Not (yet?) DOT certified.]

When I yanked the old ones out, I noticed that the filament in one of them (the one still original; made by Osram) is rather thin and the supporting wires were all covered with flakes of the filament material. Evidently, bulb operating temperatures are high enough for the filament to partially evaporate, but subsequent condensation occurs on the supporting studs, i.e. in the wrong place. That's why the filament gets progressively thinner and inevitably breaks at certain point. Given all that, I would rather blame the H7 technology than Volvo for such a high frequency of bulb failures. But then again, mine has been acceptable, no complaints.

I'll keep the list posted on the durability of the Philips VisionPlus (have 2 sets).

Cheers,

Vadim