analyse spørgsmål. hvad tror du "imprisoned lightning" betyder?

jeg er i gang med at analysere Emma Lazarus, “The New Colossus” (1883). Jeg synes det er rigtig spændende at analysere fordi der bare er så mange mataforer. Men nogen af dem synes jeg ikke giver så meget mening. fx "imprisioned lightning". jeg mener bare, hvorfor skal lyset holdes inde? er det ikke meningen at frihedsgudinden skal sprede lys? :) hvis du får en åbenbaring så skriv. 

[Inscription on The Statue of Liberty]

Not like the brazen giant of Greek fame
With conquering limbs astride from land to land;
Here at our sea-washed, sunset gates shall stand
A mighty woman with a torch, whose flame
Is the imprisoned lightning, and her name
Mother of Exiles.  From her beacon-hand
Glows world-wide welcome; her mild eyes command
The air-bridged harbor that twin cities frame,

“Keep, ancient lands, your storied pomp!" cries she
With silent lips.  "Give me your tired, your poor,
Your huddled masses yearning to breathe free,
The wretched refuse of your teeming shore,
Send these, the homeless, tempest-tossed to me,
I lift my lamp beside the golden door!”