2006 non-HID lights keep burning out

1. Measure voltage across the 12V battery when the Prius is READY. If it is too high that would be the root cause of the problem.
2. What brand headlight bulbs do you install?
3. How many miles do you drive in a year and do you leave the headlights on at all times - or not?

 

I use the lower brightness headlamps which last the longest. Brightness seems crappy though.
If you look at the lights at Walmart (for example) they show on the package chart of expected life vs. brightness.
Basically the brighter you choose, the lower the life is.
By the way, you are getting a great deal...Toyota would charge you $200 labor to change out the lights that cost you just a few bucks at Walmart.
Its pretty hard to change out the lights although once you get the hang of it it gets easier. There are some YouTube videos.

 

OK, suppose you drive 15,000 miles per year at an average speed of 35 mph. That means the lights are on 430 hours per year. Adjust this computation for your actual driving experience.

According to your post, you had last replaced the bulbs in July 2014, then in December 2014, so the bulbs lasted 5 months. That would imply the bulbs only lasted ~200 hours given my assumptions above.

This website suggests that halogen bulbs should last 450 to 1,000 hours: How long do halogen headlights last? - HowStuffWorks

This website suggests that driving over rough, bumpy roads will shorten the life of halogen bulbs. Is that how you would characterize the two lane roads that you drive upon?
How Long Should a Car's Light Bulbs Last? - KickingTires

Since you consider that leaving headlights on at all times is a safety measure, perhaps you need to accept the frequent bulb replacement as a tax that you are paying for that safety.

 

I suspect that this is your problem. Some will argue that this is not the case, but I feel that the Prius, like any other vehicle, has voltage instability (surges/spikes) when first powered on. These can shorten the life of your bulbs. If you turn the lights off before starting your car, and wait even a few seconds (5 is good) before turning your lights on, the current in the light circuit will have settled.

I had a relay fail because the coil contacts became fouled from arcing at 6 months. I suspected the contacts were chattering from unstable current during startup. I replaced the relay and also installed a delay timer relay in series before the main relay. The delay has protected the relay contacts and it has been problem free for over a year.

 

Try turning your lights off, either before shutting down, or before starting up. Then turn your lights on, after at least a 5 second delay after starting your car.

Then get back to us in 6 months to report that your bulbs are doing well.

This is assuming that your mechanic isn't fouling the bulb with greasy/oily hands. Touching the glass envelope of the bulb will cause shortened bulb life due to hot spots that will cause failure of the glass capsule.

 

...my wife insists on keeping lights on at all times.
We are still getting long bulb life anyway but we use the dimmest standard brightness bulbs.

 

I keep my lights on all the time. The first set of bulbs lasted 7 years.

 

Aftermarket bulbs last about a year. If u want long life Go to the dealer and buy the original bulbs.
My original bulbs lasted about 5 years with lights always on. The aftermarket Phillips bulbs although very bright last 9 months.

This reminds me I have 2 bulbs out so tomorrow I am going to the dealer and buy
The OEM bulbs and give them a try.

And your right i find it very hard to replace the bulbs. I did it without taking the front
Bumper down twice now and it sucks. Bumper this time.

 

if the drunken morons and texting idiots out there can't see your car in broad daylight, the headlights really aren't gonna help much. use the money you save on bulbs to buy decent horns to replace the joke "meep" oem horns.