  Clouds form on extrasolar planets and brown dwarfs where lightning could
occur. Lightning is a tracer of atmospheric convection, cloud formation and
ionization processes as known from the Solar System, and may be significant for
the formation of prebiotic molecules. We study lightning climatology for the
different atmospheric environments of Earth, Venus, Jupiter and Saturn. We
present lightning distribution maps for Earth, Jupiter and Saturn, and flash
densities for these planets and Venus, based on optical and/or radio
measurements from the WWLLN and STARNET radio networks, the LIS/OTD satellite
instruments, the Galileo, Cassini, New Horizons and Venus Express spacecraft.
We also present flash densities calculated for several phases of two volcano
eruptions, Eyjafjallaj\"okull's (2010) and Mt Redoubt's (2009). We estimate
lightning rates for sample, transiting and directly imaged extrasolar planets
and brown dwarfs. Based on the large variety of exoplanets, six categories are
suggested for which we use the lightning occurrence information from the Solar
System. We examine lightning energy distributions for Earth, Jupiter and
Saturn. We discuss how strong stellar activity may support lightning activity.
We provide a lower limit of the total number of flashes that might occur on
transiting planets during their full transit as input for future studies. We
find that volcanically very active planets might show the largest lightning
flash densities. When applying flash densities of the large Saturnian storm
from 2010/11, we find that the exoplanet HD 189733b would produce high
lightning occurrence even during its short transit.
