How did the light affect the sighting?
It is uncertain if King Arthur, who was said to have led the Ancient Britons (ancestors of the Welsh, Cornish and Bretons) against the Anglo-Saxons (ancestors of the English) ever really existed. However, he was credited with a dog called Cafall, which actually means "horse", perhaps an indication of his size. What breed would he have been?
This goes back to 1877. A "wild man" (?last of the Wodewoses?) tried to kidnap the wife of a local farmer. He was shot at, which dissuaded him from his purpose. There have been various stories of Bigfoot like creatures in England, but the country is not big enough to sustain a breeding population. This wild man may have been simply an unkempt individual or an interdimensional traveler.
The following account of a boy who claimed to be able to visit the fairy realm and who is an historical character who lived into old age, and people still remembered him as an old man in 1859.
His name was Johnny Williamson and he would visit the fairies. On one occasion, having done so, he emerged from a hole in a peat bank. He said the fairies were "his folks". He was known as the Boy of Borgue.
Source: L. Henderson and E.J. Cowan Scottish Fairy Belief East Linton: Tuckwell Press, 2002, pp. 58-59.
This was a strange doglike animal, perhaps a jackal, observed in Kent, where it attacked sheep. It was first reported from Tonbridge in 1904, later from Sevenoaks. Several of the witnesses (which were numerous) took shots at it. Its identity was never certainly discovered.