Do Orthodox believe the eternal fire is related to the uncreated light? I have been reading Welcome to the Orthodox Church by Frederica Mathewes-Green. She points out that, at the time of the writing of Scripture, artificial lighting hadn't been invented and therefore any conception of light that the church had was inevitably related to fire (eg the sun and actual fires) so describing God as light was a great way to describe something wonderful to some and terrible to others.

She also mentions (unless I'm mistaken) that Orthodox believe all beings will return to God's presence sometime in the future but that, like fire, it will be a warmth and a joy to those who respect it properly but painful and unbearable to those who don't.

Do Orthodox believe the eternal fire is the same as the uncreated light? Is there even any association?
According to the Orthodox saints, the “fire” that will consume sinners at the coming of God's kingdom is the same “fire” that'll shine with splendor in the saints. It is the “fire” of God’s love; the “fire” of God Himself who is Love. 

“For our God is a consuming fire” (Hebrews 12:29) who “dwells in unapproachable light.” (I Timothy 6:16).

For those who love God and who love all creation in Him, the “consuming fire” of God will be radiant bliss and unspeakable delight. For those who do not love God, and who do not love at all, this same consuming fire will be the cause of their “weeping” and their “gnashing of teeth.”

According to Orthodoxy, God does not punish man by some material fire or physical torment. God simply reveals Himself in the risen Lord Jesus in such a glorious way that no man can fail to behold His glory. It is the presence of God’s splendid glory and love that is the scourge of those who reject its radiant power and light.

NOTES

http://oca.org/orthodoxy/the-orthodox-faith/spirituality/the-kingdom-of-heaven/heaven-and-hell

https://orthocath.wordpress.com/2010/09/16/hell-and-gods-love-an-orthodox-view/

http://stgeorgegoc.org/pastors-corner/fr-ricks-sermons/the-fire-of-god