I found this episode really interesting! I actually have a few interesting facts that I want to add too! I did a report on Theatrical Gas Lighting in college, and this reminded me of it.
In the Neoclassical Era in French Theatre, nobles would actually be seated on the stage, to showcase their wealth. Theatre, in general, was also very "flat". Sets were often flats (think walls), that were painted to look like the given scenes. There wasn't much depth, and the theatre was about the spectacle and being seen as an audience member, as opposed to actually seeing a performance.
The advent of gas lighting (introduced in 1817 at the Lyceum, Covent Garden, and Drury Lane Theaters in London) created a marked change in the theatre dynamic. Lighting was brighter, controllable, and could produce colors with colored cellophane or the famous "limelight", the former being the predecessor to modern-day cyc lights, which create their colors with colored "gels". This advancement in lighting allowed for the onset of the naturalism/realism movements in theatrical styles; because the actors could actually be seen, their choreography became more realistic, and costumes, makeup, and sets became more detailed.
With this gas lighting, a divide developed between the audience and the performance. The gaslights likely made the theaters very warm and posed a fire hazard. As a result, the lights in the audience would be dimmed when the lights on-stage were on, thus leading to the modern practice of dimming the house when the show begins. As one could guess, the audience members could no longer see each other in the darkness, and they instead focused on the performances. This point likely marks the shift from an active audience to the passive audience of modern theatre.
I have also included a few graphics of how this gaslighting work. They can be found in Walter Grafton's Handbook of Practical Gas-Fitting and Lloyd's Practical Guide to Scene Painting and Painting in Distemper (respectively).
Editors of Encyclopædia Britannica, The. "Limelight." Encyclopædia Britannica. Encyclopædia Britannica, Inc., 14 Feb. 2012. Web. 25 Feb. 2017.
Emeljanow, Victor. "Erasing the Spectator: Observations on Nineteenth Century Lighting." Theatre History Studies 18 (1998): 107-16. ProQuest. Web. 25 Feb. 2017.
Essig, Linda. "A Primer for the History of STAGE LIGHTING." TD & T - Theatre Design & Technology Spring 2016: 10,20,22-23. ProQuest. Web. 25 Feb. 2017 .
Grafton, Walter. "Chapter XI: Theatres and Public Places of Entertainment." Handbook of Practical Gas-fitting: A Treatise on the Distribution of Gas in Service Pipes, the Use of Coal Gas, and the Best Means of Economizing Gas from Main to Burner: For the Use of Students, Plumbers, Gas-fitters, and Gas Managers. London: B.T. Batsford, 1907. 141-54. Print.
Lloyds, F. "Hints on Effects." Practical Guide to Scene Painting and Painting in Distemper. London: George Rowny, 1875. 74-87. Print.
McCullough, Jack W. "The Theatre as seen through Late Nineteenth Century Technical Periodicals." Performing Arts Resources 14 (1989): 13-58. ProQuest. Web. 25 Feb. 2017.
Pearl, Sharrona. "Building Beauty: Physiognomy on the Gas-Lit Stage." Endeavour 30.3 (2006): 84-89. JSTOR [JSTOR]. Web. 25 Feb. 2017.
Rees, Terence A. L. Theatre Lighting in the Age of Gas. Cambridge: Entertainment Technology, 2004. Print.
Wild, Larry. "A Brief Outline of the History of Stage Lighting." A Brief History of Stage Lighting. Northern State University, 14 Sept. 2015. Web. 25 Feb. 2017.