Well ambient brightness matters, but actually analog cinema projectors use a frame rate of 48 fps (they "flick" every movie frame twice), so it's still way above 30fps.
Plus, with CRTs the problem is exacerbated, because they scan top to bottom, and need higher refresh rate to hide this effect.
Plus, with CRTs the problem is exacerbated, because they scan top to bottom, and need higher refresh rate to hide this effect.