Candle

A candle was a stick of wax with a wick that was lit. The flame would gradually use up the wax as it burned, shortening the candle.

Jamie teased Zoe  when she did not recognise or understand the function of candles, a technology that she had never encountered. (DW: The Mind Robber)

Mandrel marked a level on a candle he owned and told the Fourth Doctor he must return from the Consum Bank before it burned that low or he would kill Leela. (DW: The Sun Makers)

Due to the plant's sensitivity, West Yorkshire rhubarb had to have a carefully controlled light source. For this reason, Martin Chisom used candles in his rhubard forcing shed. (ST: Lost in the Wakefield Triangle)