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.