Definition of multiple light sources in a world file

Hi guys, i need to include multiple light sources in my world file. By adding the default sun model in .gazebo/models as well as a manual defined directional light gazebo (v 2.2.3) crashes (for code see below). >model://sun This snippet causes the following error: > gzserver: /usr/include/boost/thread/pthread/recursive_mutex.hpp:101: boost::recursive_mutex::~recursive_mutex(): Assertion `!pthread_mutex_destroy(&m)' failed. Are there any example worlds with (different) multiple light sources available? Best regards!