Why do lights in a parallel circuit burn brighter than in a series circuit?

In a parallel circuit, more power is provided to the lights. Power = V2/R . The resultant resistance of the circuit is lower, and the potential difference is not divided as in a circuit in series. Thus, lights in parallel burn brighter.

Additional InformationA lamp's power rating only applies at its rated voltage. Because the voltage across each branch of a parallel circuit is the same, each lamp can be supplied with its rated voltage and, therefore, will operate its rated power. In a series circuit, the voltage appearing across each lamp will be considerably lower and, so, the lamps will not operate at their rated powers.