Janelle wants to buy some strings of decorative lights for her home. she is trying to decide between two strings of lights that are wired differently.

how should janelle’s lights be wired, and why?

If she has a choice and the wiring details are stated on the packaging,
then Janelle should look for lights that are wired in parallel within the
string, and she should avoid lights that are wired in series within the string. 

If a single light in a parallel string fails, then only that one goes out. 
The rest of the lights in the string continue to shimmer and glimmer.

If a single light in a series string fails, then ALL of the lights in that string
go out, and it's a substantial engineering challenge to determine which light
actually failed.

It equals just about 6,300 km per hour each day an week