Re: Why does only one half of the pickle light up during experiment?

Your assessment of why the pickle glows is exactly correct.  The light
is from the de-excitation of the sodium atoms.  I am unable to tell
you why only one side of the pickle glows at a time, but it is not
because of alternating current.  Alternating current changes direction 
120 times during one second.  This alternation would be undetectable to 
the human eye.  In fact, some devices, called tick timers, are commonly
used in high school physics laboratories to gague time based on alternating
current. 

The reason why only one half of the pickle glows is a mystery to me.
If you have a case where each side might or might not glow, independant
from the other side, I would hypothesize that perhaps each side must
build up enough excited sodium ions to glow, and that when it is not 
glowing, it is building up excited sodium ions.  Again, this is only a
hypothesis.

Matthew Barchok, Mad Scientist