https://www.youtube.com/watch?v=Ivy_9EmInZ0&t=530s             https://www.youtube.com/watch?v=V0AJibBtyME&t=414s 

Why on earth would you want to do this.? 

Not with crappy eBay tubes at any rate, a decent set of LED tubes look well in converted lights when done properly!

Sorry, a fluorescent fixture is designed to use fluorescent tubes. HID fixtures are designed to use HID lamps, SOX fixtures are designed to use SOX lamps. Anything else is just plain wrong.

Don't get me wrong, if you really do love LED's, I'm not going to try and stop you using them (although I'd prefer it if you didn't..!)

But don't "convert" fixtures designed for other types of lamp.

I think the replacement led bulbs used in this fixture are very poor quality because this antique fixture gives off very little light 

Why on earth would you want to do this.? 

Two or three times better efficacy compared to T12 - further increased by the fact the light doesn't need to be reflected?
Frequent switching without wearing the lamp?
100% light output in a fraction of second? (I've got some 2D lamps that run up almost as slow as HID.)
Decent tubes not readily available any more?
Longer lamp life? (I mean decent quality LEDs - not cheap ones.)

Sorry, a fluorescent fixture is designed to use fluorescent tubes. HID fixtures are designed to use HID lamps, SOX fixtures are designed to use SOX lamps. Anything else is just plain wrong.

They were designed to use those lamps because no suitable alternative existed. Now some manufacturers produce replacement LED modules for their original fixtures. I've got one and while very ugly (hidden behind the diffuser) it works perfectly.
Actually I'll probably have to convert remaining two 2D fittings if I don't find decent 2D tubes. This LuxLike crap isn't worth trying again. Very slow run up and short life.