Many examples of engineering go unnoticed because they are so much a part of
our daily lives that we rarely give them
much thought. When you decorate your
house with holiday lights, you probably do not think
about the engineering that was needed to produce
them. Holiday lights have become safer, cooler,
and more economical to produce and operate since
their invention more than 100 years ago. Here we
will examine how current flowing through a bimetallic strip causes lights to blink on and off. A bimetallic strip is made of two different thin metals—
usually copper (or brass) and steel that are bonded
together. The steel expands less than the copper or
the brass when heated, so the strip curves toward
the steel side.