This wikipedia link
https://en.wikipedia.org/wiki/Fluorescent_lamp shows how lamps are wired, tried to import image to this post but the pre-view shows just link not picture.
Around half way down under starting it has this image [img]https://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Fluorescent_Light.svg/938px-Fluorescent_Light.svg.png[/img] which shows the three main components,
1) Ballast (G)
2) Tube (F & A)
3) Starter (C, D, & E)
It does not show the power factor correction capacitor which would go where it shows (B) incoming supply.
With an LED tube the Starter (C, D, & E) is replaced with a fuse, and the Ballast (G) can be shorted out , and the capacitor disconnected, what is hoped is if a fluorescent tube is put back in on a latter date that the fuse that replaces the starter will blow.
With the fluorescent the ballast has a duel job, it gives a large voltage spike on starting to get the lamp working, and it also reduces the current once the lamp has started, without the ballast either the lamp will not light, or there would be a big bang as unlimited current goes through the tube.
There is no problem removing ballast for the LED the worry is what happens if some one tries to fit a fluorescent tube?
Both LED and Fluorescent are current dependent devices, but with the LED the current limiter is built into the tube, it is called a driver, and using pulse width modulation is controls the current to the LED's the PWM design also allows it cope with a huge voltage range typical 85 to 250 volt, so leaving the ballast in place may use extra power, but does not stop it working.
You need to look inside the fluorescent fitting, there should be a round device the capacitor often with plastic casing, which can be safely removed, this is in parallel with the supply and if for power factor correction, without it the fluorescent will register as using more power, but will still work, and the LED will register as using less power.
The ballast is bolted into the unit and is quite a heavy lump, often a steel casing more square than the capacitor, this can be removed and wires connected together or actually use it as a terminal block and connect both wires to one terminal, this will cause there to be a higher voltage to the LED tube but the PWM unit will compensate and as a result it will use less power. But once done the fitting needs marking use LED tubes only. Seem to remember when I did mine stickers were included with the LED tube.
Do remember a fluorescent tube can give 95 lumen per watt, and a LED tube 100 lumen per watt, but with the ballast still in circuit more like 90 lumen per watt, so the only way that the LED uses less power is that it also gives out less light. Often we don't need the 5600 lumen from the fluorescent tube what we want is the spread of light, so fitting a lower output LED tube is not a problem.
Today the ballast is no longer permitted, we use an electronic replacement which means the tubes last 5 times longer, there is very little delay in starting, and no flicker. With an electronic ballast you can't fit a LED tube it MUST be removed and the fitting rewired.
