[Aredhel]

I've noted that there was only one reference to the reason for the light seen by certain people/elves that harkens beck to the fairy/faery stories of old in this thread:

The essay argues that one important characteristic of an Elf-friend is to act as a link between the world of faery and the world of man.

One really has to pay attention to legend and myth, old stories of Faery-folk who gave "the sight" to mortals who served faery-kind well. Also one must pay attention to those who have otherworldly gifts, and so shine from within with the wisdom of the totality of the world - things both seen and unseen.

You will remember Legolas' surprise at seeing Aragorn shine when confronted by the Rohirrim:

'He seemed to have grown in stature while Eomer shrunk; and in his living face they caught for a moment a vision of the power and majesty of the kings of stone. For a moment it seemed to the eyes of Legolas that a white flame flickered on the brows of Aragorn like a shining crown.'

This is quite like to the shine on the brow of Taliesin, who was named such due to the glow seen on his forehead: "Behold The Bright Brow!"

Shining from within, on the brow, or the sparkle in one's eye is all a sign of inner wisdom or sight. Gildor's recognition of Frodo's language skills, as well as Frodo's polite manner is no surprise. Frodo studied with Bilbo, and gained the knowledge of other-worldy things, as Talieson did, and Bran, and Merlin, and many other tales of people who accidentally or otherwise came to know and serve the Faery.
Is it so unlikely then, that Gildor saw the "shining brow" on Frodo?

Now let this serve as a warning, too; for those that went against the Faery were punished equally as hard. For devulging the wherabouts of Faery in Mortal marketplaces, more than one had his/her eyes popped out, leaving him/her blind!
Here we are going back to the time when eating Faery-food was not a good thing to do, lest one be trapped in their world. Some were freed to do the work of the Faery in the Mortal world. Those that did were said by mortals that "had the sight" to glow from within with a strange sort of Faery-fire.

Oh, I'm going on and on, and not making a terrible lot of sense. I can certainly find you some instances of this.

Here's a shortened version of The Legend of Taliesin:

A young boy named Gwion Back was left to watch over a cauldron prepared by the Goddess Ceridwen. The liquid brewing inside the cauldron was intended for her horribly ugly son, Afagddu (Utter Darkness.) The liquid would give anyone that drank of it all knowledge and wisdom.

While Ceridwen was away, the boy Gwion fell asleep. He awoke to find that the fire was burning too hotly, and three drops of the precious liquid splashed out of the cauldron onto Gwion's finger. Sucking his finger to alleviate the pain, he absorbed all of the wisdom that had been intended for Afagddu.

When Ceridwen found out, she was furious, and set off after Gwion. Armed with his new knowledge, he turned himself into various animals, only to be pursued by Ceridwen who would turn herself into the animal's natural predator. Finally after a long chase, Gwion turned himself into a grain of wheat in a huge mound of grain and chaff. Ceridwen turned herself into a hen and ate every last grain, including Gwion. Nine months later she gave birth to a beautiful boy. Unwilling to kill the child, she set him adrift in a leather bag on the open sea.

Eventually the bag washed up on the shore near a fisherman's hut, and was discovered by the son of the fisherman, a boy named Elffin. When he opened the bag and saw the bright forehead of the child inside, he proclaimed "Behold the radiant brow!," whereupon the child answered "Taliesin be he called!" (Taliesin means 'shining brow.') He then spewed forth an endless stream of poetry, prophesy and wisdom. Elffin took him back to the hut and he there grew up into a famous bard and shaman, later serving at the court of King Arthur himself.

Now this is Celtic and Welsh wisdom; not from England, yet it had much to do later with the Arthurian stories. Certainly Tolkien would have read this. I know that there is not ONE single instance of Tolkien saying that he studied Celtic lore, however, Welsh lore is so closely related to English lore that I hardly see that he could have ignored it.

Other forms of the Taliesin Legend, including the Welsh versions state that Talieson was really Merlin, and have wonderful translations about him:

Taliesin is best known for his relation to King Arthur, mostly through the poem the Spoils of Annwfn, which details his descent on a raid into the underworld, to capture the cauldron of Ceridwen, along with Arthur, Cei, and others.

The earliest full stories concerning King Arthur and his exploits appear to be the little known Welsh tales of "Culhwch and Olwen" and the "Dream of Rhonabwy". Though dating from before the 11th century, these two stories became a late attachment to a collection of Welsh mythological tales taken from the 14th century White Book of Rhydderch and Red Book of Hergest. Together, they are known as the "Mabinogion": an introduction for aspiring poets. Though the stories have a mythological slant, a certain amount of bardic poetic license is to be expected. Their background, however, is clearly an unfamiliar Dark Age society that gives us some idea of what the real Arthur was probably like.

The poems of Taliesin are fragmentary, and known only through a few sources. It is believed however, that they formed the nexus of material for the Mabinogion.
The "Otherworld" was a domain of Celtic deities or supernatural beings such as the "Fairy People". The Otherworld was considered to be the Celtic version of heaven (or even hell to most Christian writers).

They were hidden from mortal eyes by strong Otherworld magic. They were situated in all sort of places. Some of these Otherworlds were located on the islands, the dunes, dun-hills, forests, rivers, and lakes. A grand castle or even humble cottage could be the Otherworld, which would, appeared at night for mortals, but would probably vanish in the morning.

Normal rule does not apply in the Otherworld. A year may seem to pass in the Otherworld, but in the real world centuries may have passed. Time seemed to have stand still. Nor does the people who live there, aged like mortals. They seemed to remain forever young.

The Welsh called their Otherworld - Annwfn (pronounced Annoovin) The actual cosmology is fairly complicated, but Arawn ruled a darker part of this this Otherworld kingdom. In the Spoils of Annwfn, Arthur his companions (including Cei) steal the magic cauldron of Ceridwen which brings life, from Annwfn.

Another popular name for a portion of the Welsh Otherworld, was the Caer Wydyr or Caer Wydr - the "Fortress of Glass". Caer Wydyr is similar to Tower of Glass in the Arthurian Legend, but associated with Glastonbury Tor, England. Glastonbury Tor was supposed to be the location of the "Isle of Avalon" or "Isle of Apples", the finally resting place of King Arthur.

I can only guess that Tolkien had read The Book of Taliesin, but I cannot for the life of me imagine that he ignored it. Since the Irish legends ended up being the Welsh legends, and finally progressed into the Brittish legends, one can expect he took some of the "Bright Brow" syndrome from these texts.

A note on delivery of the sight: It can be gotten by eating something of Faery origin, being touched on the forehead or eyes, or having an ointment rubbed on the eye.

Ah well, I've made a mess of this post. But perhaps it will encourage a few of us to look up The Book of Taliesin and other wonderful Celtic and Welsh texts.
Also check out the Tuatha De Danann, who followed the Goddess Dana. They were a rustic and artistic people who were said to have possed magickal skills that humans just didn’t have. When defeated by an ancient Celtic race called the Milesians, the Tuatha De Danann made their homes underground where they are rumored to live even to this day. Some of these groups have been revered as Gods and Goddesses in the Pagan tradition. These Fair Ones also became widely known as the Faeries of lore. The Tuatha were also called coincidentally: "The Shining Ones." *chuckle*