dadiOH wrote:

Probably in the top of the case.

Not if the ballast is bad

Measure them. The "T" = 1/8; eg, T-12 = 12/8 = 1 1/2" diameter.

Thanks for the T measurements.
After noting that the 16 bulbs were all 40 watts, and that the ballasts all
said T12, they're the 12/8ths of an inch type, although they sure don't seem
to be an inch and a half in diameter. They're about an inch, but they're
definitely T12 lamps, so, that 12/8ths has to be taken with a grain of salt.

Likewise, the LED replacements are not a half inch either, but they're
certainly smaller than the bigger fluorescents, so, I now know that I
definitely have T8 LEDs replacing T12 fluorescents.

In each fixture there are apparently two ballasts:
https://s13.postimg.org/kekhhvot3/04...0_ballasts.jpg

Both ballasts were of the same type, with a sticker on each saying
Universal Therm-o-matic rapid start ballast
For two F40W T12/RS lamps, high power factor
Cat No 446-LR-TC-P, 120V, 60Hertz, 0.8Amp line
Universal Mfg. Corp, Paterson NJ, Made in USA
Class P Automatic resetting thermal protected
https://s11.postimg.org/orqbysecj/02...s_40_W_T12.jpg

One ballast is humming badly, so I have identified that one bad ballast.
However, the other ballast must also be bad though, because only one lane
lights up well in that humming fixture, so, that entire fixture is bad it
seems.

I think I have these options:
1. Replace the two ballasts with T8 ballasts and put the T8 LED bulbs in.
2. Remove just the one humming ballast & see if the other lights 2 bulbs.
2. Replace the entire fixture

Recommendations on how to proceed on the one bad fixture is asked.