im assuming my 2013 HIDs are not as bright as they once were. im going to be driving in the country a lot soon and there are deer everywhere. i reached out to a company that tests and sells headlight setups and they recommended replacing the bulbs. they obviously know more than i and when i asked about the idea of the ballasts needing changed as well because of age, they said no.

are ballasts just on or off and nothing diminished as long as the bulbs get power? it would certainly be easier to just do bulbs, but figured i would ask before i order

 

I would first start with new HID bulbs and then go from there. Generally, a bad bulb ballast will just prevent the bulb from working at all. An HID bulb lumen output does diminish over time. Furthermore, your 2013 RX bulbs are now about 11 years old; so the reduced light output is maybe due to age.

 

I'd start with the bulbs as well. We replaced ours shortly after getting our RX with the Philips D4S and have zero complaints about it. This is the link to the ones we bought (it's a one pack so you'll need to buy two)
I should have let the dashcam adjust exposure and wait till I was on level ground for this video, but here's what it looks like on my dashcam.

 

Closest analogy I can give is the ballast in the florescent light bulbs. The ballast provides high voltage to start ionization process in the light bulb. Once the ionization happens the ballast is no longer in the picture. So if you are having initial light-up of the bulb issues, then there can be an issue with the ballast and if you are having issues with the steady state lighted bulb then the bulb would be the suspect.

There are other possibilities which I would suggest that you explore:
1 Haze build up on the plastic lens. You may have seen the extreme cases where they start looking yellow.
2. Dirt build up on the reflector. [most of the light comes from the reflector]. Straight out of the bulb is a fraction of the total light.
3. Human eyes deteriorate with age.
4. Alignment of the bulb ... specially the cutoff. I do not recommend adjusting it ***** nilly, [you will never be satisfied and may blind oncoming traffic].

Salim