It will provide protection from Lightning strikes for about two screens away from placement spot. 40 units of distance radius 80 units diameter horizontally/vertically and 28.28 units radius 56.56 units diameter diagonally.
To connect protection areas with multiple Rods using simple math, players should leave 14 Pitchfork counts between each Rods horizontally/vertically. Imagine each zones as squares of 56 units in length x width instead of a circle for easier comprehension. If each Rods are placed 14 Pitchfork counts between one another horizontally/vertically, it will create a protection grid with minimum excess overlaps.
(See the Console/Commands page for instructions on measuring distance; distance can be measured with a Pitchfork's 4x4 dig area).
The Lightning Rod also provides a small radius of light (but not heat) after absorbing a Lightning bolt, which is just bright enough to prevent Charlie from attacking. The light lasts for a few Days and will go dark as soon as morning comes.