God's glory is described in several places in the Bible, but this manifestation can appear like a cloud or fire. Exodus 24:15-18 reads, "And Moses went up into the mount, and a cloud covered the mount. And the glory of the LORD abode upon Mount Sinai, and the cloud covered it… (God) called unto Moses out of the midst of the cloud. And the sight of the glory of the LORD was like devouring fire on the top of the mount in the eyes of the children of Israel. And Moses went into the midst of the cloud, and gat him up into the mount." The Israelites saw God's glory as a devouring fire! But Moses walked right into it.
Later, in Exod. 33:18, 21, 22 Moses says to God, "'Please show me your glory'…And the LORD said, 'Behold, there is a place by me where you shall stand on the rock, and while my glory passes by I will put you in a cleft of the rock, and I will cover you with my hand until I have passed by'." God sheltered Moses from too much of His glory.
Your question asks about Luke 2:9, "And an angel of the Lord appeared to them, and the glory of the Lord shone around them, and they were filled with great fear." Since this wonderful event occurred at night, the Lord's glory probably included great, shining light. It doesn't say fire, as in the Mount Sinai account, so it's unlikely that was a part of the manifestation. However, the glory or bright shining was so unusual and awesome that they were terrified (see the NIV translation).
Finally, in Isaiah 4:5, "Then the LORD will create over all of Mount Zion and over those who assemble there a cloud of smoke by day and a glow of flaming fire by night; over everything the glory will be a canopy. It will be a shelter and shade from the heat of the day, and a refuge and hiding place from the storm and rain." The time period of this prophecy is when Jesus and His church are reigning. The sin or filth of Zion will by washed away by Jesus' blood and God's glory (as demonstrated by a cloud in the day and a fire by night) will provide safety and shelter.
