A multi-group brightness controllable LED tube comprises a multi-input source selector which directs electric power to the tube from a set of diversion switches inserted between a power source and preexisting ballast. The diversion switches automatically re-establish new electric current paths to supply the LED tube power and safely bypass the preexisting ballast. The LED tube also comprises a digital sub section selector for selecting two groups of SMD (surface mounted device) LED strip lights for intensity control. When first turned on, the light will be at 66％brightness. A first toggle action dims the light to 33％brightness, and a second toggle action brings it up to 100％. The third toggle will reset the LED tube to 66％brightness. The retrofitted LED tube is suitable for single end as well as double end fixtures without a complicated conversion process. Furthermore, fixtures can be reverted back to original fluorescent operation.