Dernian Rays or Black Light

Black light is a kind of light that only can be seen through special lenses made in Dernian Landis. These lenses gave the light the name Dernian Rays, but the black light is until now only found in Daleth. The rays have been seen around Hailaiga, and scientists try to find more sources as proof for the existence of other portals. They claim the black light has its source beyond the portal, and where the black light - or its shadow - can be found, a portal must have been. There are even some scientists who not only try to find out where the portals used to be, but also want to find a way to reopen the lost portals.
Of course, the black light has the attention of the Keepers of Doravor.

There are known cases in which people had fallen ill when being too long in the presence of the black light. They say it is a strange sensation they have while being there, but they are not hurt. Only weeks later, they start to spit blood and get really sick, with diarrhoea, then small, strange stonelike humps are formed on the body and the victims eventually die of exhaustion or from the bumps that will have formed inside the body as well, and sometimes destroy vital organs. The Guild of Health Workers calls this the “frisahtsbans”. The Naglani who had this sensation say it is somewhat similar to the feeling they have just before a metamorphosis, but none of them did actually metamorph. A few patients of Master Oswillan of Rhauthuz were put into spots where apparently black light was found. Some did feel a sensation similar to the rays of the Blitzermachine, others didn't. None of them was cured from their bruised splinters (see health) and all but one died of the black light disease. The Dernian Rays may cause bad vapours that affect the health.

For more information on the black light, read the scientific notes of Garwel Masvenszn.

Shadow of the black light

The scientists report to have found a shadow of the black light. It is a shadow that remains after the disappearance of the black light, and has an echo of the light itself. How this exactly works is unknown, but people have seen the shadow through some special lenses, that show where something was after it has been removed. A very odd effect, that looks like magic. The scientists however claim it to be a natural phenomenon and not magic.
Linguistic scientist say the name “shadow of black light” can not be put to this phenomenon, but the name quickly became common after a scientists took a “Shadow Lens” to the Nieuw-Gamoor Foor in the summer of 1840.