In this paper, we introduce Flashlight interaction, a new approach to light-based interaction between mobile phones and large screens by using the phone camera flashlight. Using a mobile phone as an interaction device with large screens has been explored in various projects. Mobile phones are enhanced with different sensors and provide opportunities to be used as an interaction device with other devices such as a large display. Our approach supports to set up a private-public display setting and provide simple means for interaction without a wireless connectivity. Our user study results indicate that the interaction is easy to perform and understand due to the direct mapping between the phone movement and the response on the screen.