According to baugh, what invention served to expose the artificiality of carpentered and painted stage forms?

According to Christopher Baugh, the invention of electric lighting beginning in the 1880s allowed for the exposure of the inherent artificiality of both the carpentered and painted stage forms, making them look more two-dimensional especially with respect to their three-dimensional scenic partners.

Prior to the use of electric lighting, gas or oil was used as the fuel to produce soft and gentle lighting that allowed for the blending of the carpentered and painted stage forms with the three-dimensional elements in the stage. 

It's most likely choice a, it makes the most sense in my opinion.