LOS ANGELES — Even though Teresa Palmer is a principal star of “Lights Out,” the actress said she was “scared to death” when she first screened her new film (opening Friday).

Sitting in a Los Angeles hotel suite, the Australian actress exclaimed, “I thought to myself, ‘Why am I scared? I’m in this movie!’ … But, it freaked me out!” Palmer also explained why she was drawn to “Lights Out,” an adaptation of a short film by Swedish director David F. Sandberg, who makes his feature directing debut with this film.

“It’s this simple premise,” she said. “It plays on this instinctual, primal fear of the dark that we all have. So, first there’s that supernatural element.

“But then, it also feels like a family drama, outside of the horror aspect. The film is all about these characters who are so rich in their emotions and their vulnerabilities and all that is going on with them. So I loved that as well.”

Palmer’s co-star, Maria Bello, who plays her deeply troubled mother, Sophie, couldn’t agree more. “Horror films don’t usually come complete with all of the layers you get here,” said Bello. “Frankly, if you take the horror aspect out of this movie, it can stand up alone as quite an intriguing family drama. It’s about real people and, by the way, that’s why I think audiences will find it so scary as well. These are regular people in a family with its own issues.”

Maria Bello in "Lights Out." | New Line Cinema

Maria Bello in “Lights Out.” | New Line Cinema

Palmer also noted that “health issues can obliterate families and childhoods can be completely ruined, especially if those are mental health issues.”

In the film, Bello’s Sophie suffers from severe schizophrenia. Related to that is a mysterious, clearly very dangerous spirit that may be real, or simply a figment of Sophie’s twisted mind.

As Palmer put it, her character represents something many families will be able to understand. “My character, Rebecca, has been an example of role reversal since a very young age. She’s been the mother to her mother, because her mother Sophie’s battle with schizophrenia has plagued her all her life.”

Sophie’s dependence has made Rebecca bitter and angry — leading her to largely abandon her family home and move on with her life. Only when she sees her little brother (played by Gabriel Bateman) is experiencing so much of what she experienced as a child does she move in and take charge of the situation, in order to save her brother from further trauma.

“She then becomes the mother to her little brother, much as she had mothered their own mother, years earlier.”

Asked if she herself is afraid of the dark, Palmer revealed that “my husband [actor Mark Webber] reminded me of something the other day. He told me that I had slept with the light on throughout the entire filming process of this movie. Initially I told him, ‘I did not!’ but he was like, ‘Yes, you did and it was the most annoying thing in the world!’ ”

A few days later, Palmer went home one night, having again screened “Lights Out,” and laughed as she recalled, “I told my husband, ‘Let’s go to sleep with the curtains open tonight — and let the moonlight come in. It will be nice.’

“Mark smiled and said, ‘Ah, you saw your movie again, didn’t you?’ ”

Palmer admitted that she’s a fan of horror films. “I love the supernatural ones in particular. I love UFOs and aliens and ghosts and mysterious movies. I watched ‘Unsolved Mysteries’ when I was a kid. I have the boxed set at home. So, yes, I’m definitely a fan.”

As for Bello, she has no problem stumbling around in the dark — even after watching her new movie. “I’m afraid of many things, but not the dark,” said the actress.

Yet, as for horror films? “I’m not really a fan. I saw ‘The Exorcist’ when I was growing up. It scared me so much, I’ve rarely seen a horror film since then!”