Somebody who is slow to see the light. Flouresecent lights in India, usually in "tube" form, employ an electrical device known as a "choke" used to get the voltage and current levels up in the tube to the point at which fluorescence occurs. Typically it would take 3-4 cycles for this to happen, with the blinking on and blinking off. Therefore the phrase "tubelight" came to mean somebody who was slow to see the light

It is used to describe a person with very less perceptive power. That is slow in understanding what others say. The word comes from the "tubelight" which is a flickering fluorescent light, slow to turn on fully.