Corrected entry: Throughout the entire movie, various occurrences are seen of electrical lighting in the Opera Populaire. For example, the lamp Madame Giry turns on just before she begins to tell the story of how she rescued the Phantom. Phantom of the Opera is supposed to take place in the 1870. However, Edison did not first invent the light bulb until 1879. Hence, the electric lights would have been impossible.
Xofer
12th Feb 2005
Correction: In the case of Mme. Giry turning on the light, she's turning up the gas in the lamp, making it burn brighter.
Xofer