So, you parked in a marked-out bay, and the sign suspending parking was on a lamppost right beside your car. I'm afraid stating that you didn't see the sign, will stretch your credibility with an adjudicator. Of course, it was dark, although with streetlights, and you got home no doubt tired and ready for bed, but this argument won't get the PCN cancelled, I'm afraid.
However, the suspension sign was on a lamppost, and there is a parking restrictions sign for the bay a bit futher along. The suspension sign should have been mounted on the pole holding this sign. Was there a sign there as well ? If not, they have failed to sign the suspension correctly, but to win on this you'd need to take them to London Tribunals with the full PCN penalty in play. The adjudicator might well say that if you can't read a sign right by your car, whould you have seen a sign on the correct place ? So not a guaranteed win.
