Re: How do blinking Christmas lights work?

Good question.
The answer is that there is a single blinking light in the string of 
christmas bulbs.  This light is constructed of two pieces, one of them 
probably a bimetallic strip which is sensitive to heat.  OK, this light is 
the first in the string of bulbs.  The key thing is that this blinker is 
wired in series with the rest of the lamps, and all of the lamps are wired 
in series.  When current is initially applied, the two pieces within the 
blinker bulb are initially cold and make electrical contact.  Then all the 
lights come on.  As the blinker bulb elements warm up, the bimetallic strip 
starts to bend (because of the difference in thermal coefficients of 
expansionn).  When the bimetallic strip bends enough, the contact is 
broken, all of the lights in the string go off, and the current is 
interrupted.  This allows the bimetallic strip in the blinker bulb to cool 
off and when it has cooled sufficiently, the contact is remade and all of 
the lights go on again.  Think of it as a slow electromechanical 
oscillator.