If you end up at the tribunal, what is important is the fact that the end of lease condition report was signed off by the agent without listing a problem with the light fitting.
Objectively it is clear that a problem may or may not have arisen after the end of lease inspection. That is, the landlord is trying one on you.
I suggest you do nothing other than refer him to the above mentioned condition report.
I can’t see him able to justify to Fair Trading or the Tribunal your liability after you were cleared of liability via the condition report.