This is a weird one;

A lamp at the top of Elizabeth Tower - which is switched on in the evening whenever Parliament is sitting - is to stop shining for the first time in more than 70 years. The Ayrton Light, located above the Great Bell - known as Big Ben - needs to be fully dismantled and restored. A temporary light will replace it. Installed in 1885, it was previously turned off only during both world wars. Big Ben will not chime regularly until 2021 because of repairs to the tower.

Does it take four years to replace a light bulb?!

http://www.bbc.co.uk/news/uk-40985192