People keep using the term "gas lighting" as a synonym for "lying". There's a lot more to the concept, as I will explain, and Matthew Martin will illuminate ... The 1944 movie Gaslight is set in London at a point in history when electricity

had not reached most homes. A husband is trying to convince his wife she is going mad, that she should not believe her own eyes and ears. One symptom is she keeps seeing the gas lamps in her home growing dimmer and brighter. Here’s the plot:

A 14 year old girl disturbs a man trying to steal the jewelry collection of her aunt, a famous singer. He has murdered the aunt but escapes without the jewels.
The girl grows up to be Ingrid Bergman. She marries a charming older man who

suggests they live in the aunt’s house (which she has inherited), to help her get over the trauma she experienced there. Weird things happen, but the fluctuation in the illumination must be just her imagination.

Husband suggests she stay inside until she can become sane. Fortunately she has met a Scotland Yard detective who was an admirer of her aunt. He works out her husband is the aunt’s murderer, still seeking the jewels. The lights were going up and down

because hubby was using the lamps in the attic while rifling through the aunt’s stored belongings. Detective ties up husband in the attic, and wife gaslights him with a knife, which she would use on him if she really was mad.