This data come from the Blitzortung lightning detection project, full map can be found here:
http://www.lightningmaps.org
If you would like this as an overlay for GR Level 3, add this to your placefile manager:
http://www.k5ktf.com/sparks/placefile.txt
(in GRL3, click top menu WINDOWS, click Show Placefile Manager; Click the + and enter http://www.k5ktf.com/sparks/placefile.txt)
More placefiles can be found here:
http://www.redteamwx.com/grlevelx.html