In Hebrew these terms mean “light” and “perfections.” They were the twelve precious stones, when in position in the breastplate of the high priest, were consulted as an oracle. They were worn when the high priest entered the Holy of Holies (Exodus 28:30). The ceremony of placing the engraved gems in their proper position in the breastplate was very solemn and imposing, for it typified the twelve tribes before the altar of Jehovah. A.G.H.
Source: 80, 318.