Select an area with the Lamp Placer tool and let there be lamps.

An algorithm will place lamp-ghosts where there is electricity and no other lamps nearby. Then your robots (if you have them) will start to build the lamps for you.

Version 0.17.0:
- Update for Factorio 0.17

Version 0.16.1:
- Add per-player mod setting for distance between lamps