The fine historical novelist Elizabeth Chadwick has posted an excellent essay about medieval lighting on her site.
I have very little to add to that except that once upon a time, in the interest of research, I lived by candlelight every evening after supper for quite a few evenings. I had the advantage of good candles, which many ordinary medieval people did not have, but the experience was still extremely useful. The room became full of soft shadows beyond the gentle, rich, golden glow of the candles. As few as three slender candles provided enough light by which to read, and – here is a point I came to cherish – I found myself relaxing in the candlelight, easing out of the day’s tensions far more easily than usual, so that I went to bed much earlier than was my wont and sleeping very well.
Added to that, I am now far more appreciative when I flip a switch and simply get all the electric light I want. There is nothing like research to help you enjoy the commonplaces of the 21st century.