Q2's source should be directly connected to the 12V supply (no lamp there).

When S1 is closed, Q2 turns on, pulling Q1's gate voltage to ground.
This turns on Q1 and energizes the lamp connected between Q2's drain and ground.

 

That is not a part of any assignment. I am trying to build a DALI controller for lightning and I require to control 18V with 3.3V logic. My apologies, let me upload the pictures again:
View attachment 179687

View attachment 179688
With this configuration, the lightbulb is also constantly ON and doesnt change if I press the switch

To model a real power MOSFET like an IRF530 you need to change the N MOSFET specification in your simulation.
Try VTO = 4V and what is more important set Kp at Kp = 4 A/V^2