I have an LED torch that will run for 50 hours on a single AA. And I have lots of AAs. I can recharge from the car, and potentially solar power if it's summer. I see light as pretty much a solved problem.

I also have some candles and tealights, but they date back 10 years or so, to before LEDs got so good. Tealights I've found are especially poor, putting out about 1/3rd the light of a proper candle. Candles aren't especially good either, being rather bulky. (They can also melt in hot weather, but that's not an issue in the UK.)

Candles are also a fire risk. If you use them, make sure you have a good candle-holder. Regardless, during a black-out don't be surprised if your neighbours have fires.

I guess the main advantage of candles is they are immune to EMP, if you see that as a serious threat. And they do have a long shelf-life.