Florescent to LED replacement

[off-track]

I picked up a GE F15T8 direct swap LED bulb for my son's RFM pinball last week and it really made the backglass/translight pop!  Then I looked at the S-2000 and it looked sad.  Not knowing any better I went and got three more for it.  I don't recall seeing anything posted here but... they didn't work.  From some Googling it appears that they require a minimum of 55V and in this case I'd need a "marine" bulb as the ballast is only putting out 24V.  Is this correct?  We did measure 24V to the input side of the ballast.  I'd always expected 120V for a florescent.   

The bulbs worked just fine in the S+ so at least that money wasn't wasted (a little too bright for the above reel light though).

Attached is a pic of the ballast.  I wasn't aware that there is a difference.  I thought that a "F15T8" would be the same as both specified 15W on the bulb  itself.  Looking at my GK belly light I see it has the same ballast.  Is there a recommended replacement bulb or should I just look for 24V LED strips, wrap the original bulb and tap off the ballast input wiring directly?