A programmed start ballast would work best for these lamps to ensure the longest potential lamp life.

I'll look into obtaining the proper ballast for my 18w PL.

In that case, an electronic ballast designed for these 18w G24Q2 PL-C CFL lamps would work pretty well or you could even use an 18w G24D2 2 pin PL-C magnetic preheat CFL HX autotransformer ballast in conjunction with an external FS4 starter to run them as well.

I assumed that it would shorten lamp life. I won't run it often, since I'd use it only if I wanted a warmer 3000k over the 4100k of my other 26-42w PL's.

That lamp will suffer a reduced life on a 26w-42w PL-T electronic CFL ballast because 26w-42w PL-T CFL lamps run at a current of 0.33a while 18w G24Q2 PL-C CFL lamps run at a current of 0.22a.

18w PL-C with the G24q-2 base.

Are you talking about 18w 2G11 PL-L lamps or 18w G24Q2 PL-C lamps?

So I have an 18w (i know, bad idea) PL on a 42w PL ballast... will it be EOL faster?

@Mandolin Girl - I find just getting a clear photograph of the fixture in question and posting it to the gallery usually gets a ID aside from the really obscure stuff I've posted.

I finally decided to try and revive my dead 50w MV lamp by means of adding a 35w HPS ignitor to the circuit and even though the lamp struck, the mercury didn't vapourise and the lamp remained pink instead of warming up and turning white. I let it run for about 5 minutes and that's all it did. The lamp didn't even get warm to the touch and it still won't strike on it's intended gear. I'm still deciding if I want to try it again and let it run longer.
Here is what happened when I tried it.