Welcome to the board! Get
these D1S bulbs. HID bulbs like yours do deteriorate (get dimmer and dimmer) with runtime, but if you're talking about them being very dim compared to halogens you might have problems that go beyond just old bulbs. Lens condition is an easy one to check: if your headlamp lenses are at all cloudy, foggy, hazed, yellowed, crazed, or notably pitted, there is no bulb that will overcome that damage and you're in the market for new headlamps.
Harder to check is the condition of the reflectors. They're not visible behind the projector lens, so you can't really check them without disassembling the headlamp (which in most cases would ruin it). Here's what happens: the reflector, because it is small in a projector lamp, is physically close to the bulb. That means the reflector runs relatively hot, and eventually its shiny coating oxidizes or even flakes off. When that happens, you get a correct-shape beam pattern on the wall but there's very little light in it. This, too, would call for new headlamps.
Whether your lamps are new or old, their
aiming is crucial to your ability to see. Make sure it's checked and adjusted
correctly as per the details at the link.