What are the light sources that you have had to use when reading.

First of all, this is an electric lamp (LED or incandescent lamp), the light of street lamps, lamps in a bus or subway. When the electricity is cut off in the house or in the country, you can read by the light of a candle or a flashlight, and in some houses there are even kerosene lamps. But this is not the best way, because reading with a candle or a flashlight spoils the eyes. You can read it by the light of a fire. And, of course, you can read during the day when the sun is shining, this is the best and completely free source of illumination.