The dating of events before the rising of the Sun is difficult, and that is especially true for events as far back in history as these. The dates shown here are based on those given in The Annals of Aman in volume X of The History of Middle-earth, but the dating there is not exact, and the conversion of Valian Years into solar years introduces another level of uncertainty.

Specifically, those annals date the raising of Illuin as the 1,500th Valian Year of the Valar in Arda (or shortly afterward) and its destruction as the Valian Year 3,450 on the same system. One Valian Year is equivalent to approximately 9.58 solar years (at least on the conversion system used here), producing the figures shown above.

Though these dates are approximate, they give some idea of the vast scale of time involved: Illuin stood for more than six times the length of the entire Third Age before its downfall.

The element 'il-' literally means 'all, everything', but had an association with cosmic features that surrounded or encompassed the world (as in Ilumrambar the Walls of the World, or Ilmen the highest of the airs). Luin means 'blue', so the name Illuin seems ro mean something like 'blue Lamp that shone from the high airs' (or perhaps more simply, 'sky-blue').

We have very little information about the precise location of the Lamp Illuin. The map shown here is based on Sketch Map V from volume IV of The History of Middle-earth, though that old map is of limited usefulness in this context. The map does not show Illuin itself, but it does mark the location of the Sea of Helcar, which is elsewhere said to have been in the place where Illuin had once stood. The location shown is therefore doubly approximate.