There are two main varieties of LED tube lights - Ballast Compatible, which work with the existing fluorescent fixture ballast in place, and Ballast Bypass, which require the ballast to be bypassed or removed. Choose a Ballast Compatible LED fluorescent tube replacement for a direct swap, plug and play led tube light.

Ballast Compatible: Very Easy plug and play installation

Ballast Bypass type LED tube lights are extremely easy to install - just unscrew the fluorescent tube, and screw in the T5 or T8 led fluorescent tube replacement. They are true plug and play led tubes lights.

If the ballast in your light fixture burns out, Ballast Bypass LED tube lights can still operate, once the light fixture ballast is removed or bypassed. This is why they're sometimes called Universal - they work with a working ballast in place, or with the ballast removed, and powered directly by household wiring.

Ballast Bypass: lower cost, but requires bypassing / removing ballast from light fixture

Ballast Bypass LED tube lights are slightly lower cost than Ballast Compatible LED tube lights, but require the light fixture ballast to be removed or bypassed before they can be used. The ballast is an electronic component which regulates the electrical current in fluorescent tubes. LED tube lights do not require a ballast, since they can be powered directly by household wiring (on any voltage between 75V and 280V).

Bypassing the Ballast results in 20% energy savings

Bypassing the ballast has the added advantage of saving you money by being more energy efficient - a typical 4 foot long LED tube light will consume 22W if used with a ballast, but only 18W if the ballast is bypassed. This is true for both Ballast Compatible LED tube lights, which can be used with or without a ballast, and Ballast Bypass LED tube lights, which can only be used with the ballast bypassed.

This is from BBS