Russ,
I have on standard bulb and one Whelen Quartz bulb in the cowl of my 152. I lost count after the third standard bulb was replaced while the Whelen lives on. I used to order a landing light ($25 ea.) for every two oil filters I bought. I tried horizonal vs vertical and could not see any significant improvement in the bulb life. If the bulb is in the cowl, it's worth it to me to pay $75 and be able to depend on it.
I bought mine from Gary Bufkin at Aero Supply in Texas.