Trying to replace 1988 t12 w/ led 4ft bulbs
The "Substitube" name suggest it's made to work with an existing ballast present, and in fact the data-sheet confirms this positively.  You will need to install a rapid-start or programmed-start ballast to use these tubes.  I wouldn't do that; I'd return them! 

What surprises me is that you direct wired to the opposite ends of the fixture, without a data sheet or diagram instructing you to do so.  A guess?  Or was your old ballast instant-start with shorting lampholders (the two fluorescent pins are internally connected in the lampholder)?  The problem is that only some LED tube replacements want that configuration... many others want both hot and neutral at the same end (and nothing at the other).  Obviously this does not work with shorting lampholders.

If so, you have two choices: 


keep your wiring as you did it, and shop smartly for LED tube replacements which want line power on opposite ends.  
grab whichever direct-wire LED tubes are convenient, and then if they require it, rewire power onto the same end -- this will necessitate replacing lampholders if you have shorting lampholders.  Lampholders are about 75 cents each at a variety of places; I shop at 1000bulbs.com.  


I for one prefer wiring the opposite ends. Those two pins are only 1/2" apart, and I think that's too close for 120V (or 277V, yikes!)