Electric light
From Kerbal Space Program Wiki
A light is a part that use electricity to shine a light, they can be used to help with landing at a dark side. Currently, there are only three light sources. The Illuminator Mk1 and Illuminator Mk2 are the only light available while the Small Gear Bay also holds a lightsource. For tidally locked moons like Vall or Ike those are recommended, as one night might be very long.