I saw this color movie in the late 90s on VHS. My memory is that it feels like it’s from the 70s or maybe the 90s. It feels a bit too low-budget art-house to be from the 80s. Maybe the 60s.
The protagonists were a boy and girl, fraternal twins. I believe they were brunette, and the girl had long hair. The girl was older. They are late teens or early twenties for all but the beginning of the film.
The boy is treated really awfully, abused really, by–their parents? The twins may or may not have killed them–they leave. The boy barely speaks (he’s traumatized) and is the most angry. He invents a machine with a light bulb on it, that when you turn it on, the light starts flashing and whoever’s watching becomes fixated on it and hypnotised.
They wander around getting revenge on people from their past (I don’t remember why their victims are evil but they are) by tricking them into watching the light, and then telling them ways to off themselves.
That’s mostly all I remember. I feel like the kids wear white, or at least the girl does. I vaguely remember some scene towards the end where they’re sitting on the bank of a body of water. I remember the girl starts to become concerned about her brother’s mental state, maybe.
It’s not the kind of horror movie that’s particularly realistic–there’s no cops, no news–it’s more of a self-contained, dream-esque (to some extent) or allegorical kind of film, although certainly set in a kind of “real life.”