The intensity of Light seems to play an important role in some forms of Passage to the Obscure Cities. The lightning system in the A.Desombres Museum was controlled by a timer to avoid an overload that would have turned the frescoes into unwanted warps. The flashbulbs of Vigoleis Koelber generated exactly the required wavelength 1). It was the light of the rising or setting sun that allowed access to Mount Analogue in our world. In Urbicande, daylight was subject to a strange refraction phenomena 2). “Light Baths” are considered therapeutic in Sodrovno-Voldachia 3). The names of scientists from our world who have worked on light are known to the Obscure people, which would tend to indicate that some manipulations can open a Passage. The Hollow Earths apparently all have a powerful source of light at their core 4).