Direct Wire LED: T12 Replacement
A fluorescent light is an arc-discharge light (like neon, sodium, mercury vapor and metal halide).  There's a tube of gas and cathodes on each end.  It takes a high voltage to strike the arc, and a less-high voltage to sustain it. 

4-foot T8 and T12 tubes have 2 pins on each end of the tube. They connect a small incandescent style filament, whose job is to preheat the cathodes to reduce the strike voltage and ease wear-and-tear on the tube.  Instant-start ballasts ignore this filament and use an extra high voltage to strike the arc. 

Some LEDs want 120V on 2 pins on the same end, and the other end is a dummy.  On those, if you put a real fluorescent in there, you can expect a Pop! as the filament burns out.  

Since you got the powered on opposite ends type of tube, I would expect nothing to happen.  The strike voltage of a 4' fluorescent tube is significantly  above 120V, especially without preheating.