Lights and perfections, or light and truth; a divinely appointed means of "inquiring of the Lord," its name being expressive perhaps of the truth of his revelations. It would appear, though not certainly, to have been made known to the Jews at some time prior to its first mention in Scripture, Exodus 28:30. It had some connection with the high-priest's breastplate, Le 8:8, and perhaps is to be understood as present when the ephod is mentioned, being worn on the outside of it, Numbers 27:21 1 Samuel 23:9,11 2 Samuel 2:1.

It is spoken of in the following additional passages, De 33:8 Joshua 7:6,15 1 Samuel 28:6; and last of all in Ezra 2:63 Nehemiah 7:65. Some think it was the precious stones on the sacred breastplate, which made known the divine will by casting an extraordinary luster. Compare Exodus 39:8-14 Le 8:8. Others assert that they were the words Manifestation and Truth, written upon two precious stones, or upon a plate of gold. Various in fact are the conjectures upon this subject, and Moses has nowhere spoken of the Urim and Thummim in such terms as to remove the obscurity. When this oracle was to be used in inquiring of the Lord, if at Jerusalem, the high-priest put on his robes, and going into the Holy Place, stood before the curtain that separated the Holy Place from the Most Holy Place; then, turning his face directly towards the ark and the mercy-seat, upon which the divine presence rested, he proposed the subject respecting which he desired "light and truth." See BREASTPLATE.

The Third
... Besides these stones there were the stones of the "Urim and Thummin," of
which little or nothing is known. These may have "white ...
//christianbookshelf.org/bullinger/commentary on revelation/the third.htm

Retiring Before the Sanhedrin's Decree.
... In earlier, better days the high priest had represented the divine headship of the
nation, and through him, by means of the Urim and Thummin, the inspired ...
/.../mcgarvey/the four-fold gospel/xciv retiring before the sanhedrins.htm

The Best Beloved
... How charming to view him as a priest, with the Urim and Thummin, wearing
the names of his people bejewelled on his breastplate! ...
/.../spurgeon/spurgeons sermons volume 24 1878/the best beloved.htm