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    | • | Light energy can
    be absorbed and emitted by 
 |  | 
   
    |  | promotion and
    relaxation of electrons from one 
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    |  | energy level to
    another--see a line in spectrum 
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    |  | corresponding to
    energy difference (photon 
 |  | 
   
    |  | emission) btn
    levels. 
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    |  | 
   
    | • | Don’t see all
    colors, just those that correspond to 
 | 
   
    |  | energy difference
    btn levels 
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