In the directory where the xLights.exe is found should be a xlights.windows.properties file. You need to edit that (notepad should be fine). Change the lines:
log4cpp.category.log_opengl=INFO, A1
log4cpp.category.log_opengl_trace=INFO, A1
to
log4cpp.category.log_opengl=DEBUG, A1
log4cpp.category.log_opengl_trace=DEBUG, A1