Lightning density can be set in 2 ways :

• Through statistical analysis of specialized organizations (Météorage en France), for several years. These data are often payable and are accurate as they provide the lightning density at the scale of a city.
• Through lightning maps available in the standards.

Keraunic level and lightning density

The study of lightning protection requires the consideration of local geographic conditions, in particular the degree of exposure of the structure to the risk of lightning  in order to size the necessary “power” of the protection devices   to winds considering its architecture in order to determine the necessary mechanical strength of the devices to be installed.

NK KERAUNIC LEVEL

 Nk keraunic level shows the average annual value of the number of thunderstorms days (days when thunder is heard in a given place).

NG LIGHTNING DENSITY

 Ng lightning density  shows the average annual value of the number of lightning strikes per km². In France, the lightning density values are determined by the Météorage network. When the density is not known for a given site, it can be deduced from Nk according to the following relationship.