I had cables coming out of the wall which were meant for a lamp. I asked a friend of mine who is an electrician to connect the cables to a switch I had below the cables.
I bought fairy lights which can be connected directly to electric sockets and cut it into 3 parts for the 3 Tetrominoes. Then I threaded the cables through the related holes and reconnected them using luster terminals. Be sure to put soldering tin on the cut ends to get stable cable ends for the terminals.
After that I connected the fairy lights to the switchable cables, which came out of the wall, again using luster terminals and mounted the TetrisLamp on the mounting screws.
On the last image you can see the TetrisLamp in action. It' s just a raw realization. I want to create another one which is on a higher level of quality. The described one is just a kind of prototype.