Lights flickering

[Tea3]

Hi people, how's everyone? What's the possible cause for flickering lights? When my car is idling at night i.e. at traffic lights, I notice the car lights flickering a lot & engine feels like dying/not enough energy or power. Feels fine when I am driving. I have a relatively new battery & spark plugs. Water pump has been changed - not leaking anymore. The only other thing that is in my mind is the alternator. Any other components in the car that somehow connects the engine to the lights?

Another thing, my car idles sometime above ten, sometimes below ten without the air con switched on. Why? Shouldn't it be consistent?