London has more than 1,000 gas street lamps, which were installed at the beginning of the 19th century.
At the time, they were considered a major innovation in a city with dark, dirty and often dangerous streets.
In central London, they still light up parts of The Mall avenue leading to Buckingham Palace, the back streets of Covent Garden, and around Westminster Abbey.
The atmospheric light they give out is evocative of Charles Dickens novels, Mary Poppins and Sherlock Holmes.
But as they become increasingly difficult to repair and maintain, local councils are considering replacing them with eco-friendly LED ones.