In Heisig's book Remembering the Kanji, 16th edition, kanji #519 (暗) is named Darkness. In Yu-gi-oh however the darkness element uses 闇
According to the following link, 暗 does indeed mean dark, darkness. The same site mentions the added meaning of gloom to 闇: https://jitenon.com/kanji/%E6%9A%97
Why are there two kanji with the same basic meaning and how would I know when to use one or the other?
Are there implied differences that can be inferred without actually explaining by using one versus the other?