Guess what light this is...

[Mike]

Oh yeah maybe the others are CX41 and not SPX41... I don't know lol...

[GEsoftwhite100watts]

This brand/era of ballast tends to have capacitors go bad, reducing lamp current and eventually not lighting at all:

[Mike]

Therm-O-Matics or 80s Advance ballasts.

These ballasts tend to overheat and spew tar all over the inside of the fixture.

[GEsoftwhite100watts]

80s Advance.  I personally joke any post-80s Advance ballast has an "Advanced" failure rate compared to other brands, which is annoying since they're the most common it seems!
A GE Bonusline! I have one like that, but it still works, and is used every day for long hours unattended as a plant light.
These "Thump" when turned on  then "Chatter" if the lamps are cold.

[Mike]

Hmm funny thing is that I never come across those Advance ballasts. I tend to keep finding Universal or magnetek ballasts lol.

Slimlines.

These have the most interesting warm-up phase compared to any other HID IMO.

[GEsoftwhite100watts]

Older HPS lamps which start grayish, turn mercury blue-green, then xenon white, then pinkish, then LPS monochromatic yellow, then slightly whiter with slightly better CRI.
Pre-mid 90s T12 fluorescent lamps made by this big-3 brand blacken heavily before actually dying.

[Mike]

Yeah HPS lamps have a cool warm up in general. Older MH lamps are interesting too.

GE.

This company's T8 tubes blacken a lot before dying...

[GEsoftwhite100watts]

GE!
This is my favorite fluorescent color temp:

[Mike]

5000K 90CRI

These are my favorite two color temperatures (with 800 Series phosphors)

[GEsoftwhite100watts]

3500K and 5000K
This is my favorite fluorescent size:

[Mike]

F96T12 slimline? Or F40T12?

The first vintage fluorescent fixture I ever got:

[GEsoftwhite100watts]

Both of those too but the 8' slimlines in particular.
A vintage shoplight with a Universal Therm-O-Matic ballast rated only for 40w lamps from February 1973 that you've since totally repainted and have hanging in your basement. 

[Mike]

Yep.

[GEsoftwhite100watts]

This is the highest-wattage light I use in my home:

[Mike]

400W MH?

This is the most recently made street light in my collection, made in 1997.