Gaslight (1944) is a film directed by George Cukor adapted from Patrick Hamilton's 1938 play Gas Light. It stars Ingrid Bergman, Charles Boyer, Joseph Cotten, and, making her screen debut, the 18-year-old Angela Lansbury. It's terrific.
But it's not a patch on the original British production, directed by the greatly undervalued Thorold Dickinson (1903-1984). To my delight this version is currently available to watch online (but has so far attracted fewer than 300 viewers). It's a brilliantly atmospheric and chilling tale of a fragile woman manipulated by a cold husband into believing that she is going mad. Find the time to watch this, and switch all the lights off when you do.
Anton Walbrook! He's one of my favourite actors, not least for his superlative performances in two of the greatest Powell & Pressburger films - as the good German Theo Kretszchmar-Schuldorff in The Life and Death of Colonel Blimp and the Diaghilev-like Count Boris Lermontov in The Red Shoes, a very sexy maniac.
A later Dickinson film, also starring Walbrook, is The Queen of Spades (1949) adapted from the Pushkin short story. Not available online, alas. It features Edith Evans (in her screen debut) as the aged countess who sells her soul to the devil in exchange for virtuosity as a card player. Look out for this.