This is a term used to refer to someone that's observed or analysed something that has already been implied or is obvious.
Commentator of a game: Mumbai Indians lost the match due to their poor batting display.
David: Mumbai could've batted better.
David's friend: Why does this guy give his tube-light analysis all the time
Someone who takes a long time to get something...i.e. he/she is slow. The word's short form is tubie...it literally means a florescent bulb... because when you switch it on the light doesnt actually flash until a few seconds later. Similarly, the person's brain whom you called a tubelight, doesn't light up and understand something until later
Rose is such a tubelight, she didn't get the joke until after everyone stopped laughing
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.