Rinxo Jabbery was a Lucerian student who was investigating human culture for his thesis in the 45th century. As part of his research, he visited Stockbridge. When Nyssa and Lysette Barclay went into the crypt, he used his bioluminescent proteins to create light. (AUDIO: Plague of the Daleks)
This light was often used in mating rituals. (AUDIO: Plague of the Daleks)
Rinxo also mentioned that Lucerians had visual capabilities that were superior to humans, which why was Rinxo could distinguish a light at the end of a long, dark passage that the others could not. (AUDIO: Plague of the Daleks)