This historical Australian newspaper article contains the keyword "mystery light": 19 Jul 1913, "LAKE LIGHTS MYSTERY. THE EARL OF ERNE ON "WILL-O'-THE-WISP" THEORY.":
http://nla.gov.au/nla.news-article98413256
LAKE LIGHTS MYSTERY. - THE EARL OF ERNE ON
The Earl of Erne is not greatly impressed by the "will-o'-the-wisp" theory of the mysterious lights seen in Ireland, particularly in the neighborhood of Lough Erne, Country ...
Trove