Transmitting information with visible light requires controlling the intensity of the light source. Many light sources in our environments, however, cannot be controlled (not only the sun but also plenty of light bulbs). These uncontrollable light sources provide an immense amount of ambient light that could be used for wireless communication, yet few studies are exploiting this opportunity. We provide a detailed analysis of a Hardware- and Physical-Layer to create safe and reliable wireless links relying solely on ambient light and simple photosensors. Motivated by recent studies, our platform builds upon liquid crystal displays (LCDs) to backscatter ambient light, but it provides a unique and novel feature: our platform utilizes frequency signals to modulate ambient light. Compared to the state-of-the-art, which rely on either pulse- or color-based modulation, our approach allows us to provide simultaneously: a simple and energy-efficient platform (no cameras), flicker-free communication (safe), and the ability to work reliably in spite of the interference and light fluctuations caused by uncontrollable light sources (reliable). We test our platform in indoor and outdoor environments, and show that an LCD surface of 6×8 cm can transmit 80 bps at ranges between 4 meters (indoors) and 60 meters (outdoors), consuming a fraction of the energy required by comparable systems using cameras.