A lightning rod structure comprises a steel rod for connection to the ground, the rod extending upwardly from a central hub, and the structure further including an accelerator associated with the hub. The accelerator includes upper metal deflector arms radiating from the hub and each formed with a series of holes, and further arms of dielectric material radiating from the hub below the deflector arms. The further arms carry upwardly extending exciter needles centered on the holes in the upper arms. In use, a potential difference is created between the rod which is positively charged and the needles which become negatively charged.