  Lightning was detected by Voyager 2 at Uranus and Neptune, and weaker
electrical processes also occur throughout planetary atmospheres from galactic
cosmic ray (GCR) ionisation. Lightning is an indicator of convection, whereas
electrical processes away from storms modulate cloud formation and chemistry,
particularly if there is little insolation to drive other mechanisms. The ice
giants appear to be unique in the Solar System in that they are distant enough
from the Sun for GCR-related mechanisms to be significant for clouds and
climate, yet also convective enough for lightning to occur. This paper reviews
observations (both from Voyager 2 and Earth), data analysis and modelling, and
considers options for future missions. Radio, energetic particle and magnetic
instruments are recommended for future orbiters, and Huygens-like atmospheric
electricity sensors for in situ observations. Uranian lightning is also
expected to be detectable from terrestrial radio telescopes.
