Originally Posted by Wuzzat?
Use an Underwriter's Knot to strain relief the cord
and make sure that the socket shell connects to the long slot on the plug (the cord with the stripe or the ribs)
and that the lamp switch switches the other smooth conductor on the cord and that the cord wraps around the screw so that
as the screws tightens it wraps the wire tighter rather than tending to loosen the wire.
For long life observe max bulb wattage which may depend on the socket being below the bulb or above.
And even if you did everything wrong, or had a flipped coin decide this issues for you, the lamp would still 'work' for a while.
Originally Posted by tomsmyth
Why does polarity matter for a lamp?
It matters for grounded people who may touch the lamp shell which is more exposed that the lamp center contact.