Light is electromagnetic radiation that can be perceived by the human eye. It ranges from the infrared with longer wavelengths to the ultraviolet with shorter wavelengths (about 750 to 380 nanometers). In contemporary cities, artificial light at night usually has a positive connotation. It is associated with progress, safety, beauty and vibrant cities. But there is also a growing awareness of its disruptive effects on ecosystems and living species, including humans. How do people learn to be affected by ‘light pollution’? How do light waves become a public concern?