The only time I have ever seen this reading for moon was with the Japanese pronunciation of the Death Note character, Light, who's first name is written with the word moon. I want to know if the reading "raito" for moon was used before Death Note was created or did the author specifically made up the reading to name their character after?
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No, the main character of Death Note might be the very first person with the name 月【ライト】 (although there is no way to confirm this).
Of course no dictionary says "月" can be read as ライト. But in Japan, it is legal to name a person using simple kanji, and specify its readings freely. If they really wish, parents can ignore what kanji dictionaries say about readings.
Typical Japanese "unusual names" (DQNネーム/キラキラネーム) are those which look like normal Japanese words but their readings come from Western words, such as 「火星【マーズ】」 or 「不死鳥【フェニックス】」. Those unusual names do happen occasionally in reality, but in manga and games, authors often create strange names to avoid conflict with real names or names from other works.
As for 月, I wouldn't be very surprised if there were a few real people somewhere in Japan with unusual names like 「月【ルナ】」 , 「月【ムーン】」, 「月女神【アルテミス】」. 「月【ライト】」 is also legal, but "月" and "ライト" (either it's right or light) has no direct link, so I doubt if there was a person with such a name before Death Note.
I can't say anything authoritative about whether it has ever been used that way, but at least based on this site that lists unusual names, people seem to be very surprised that someone might actually use that name for someone.
Outside the context of names I do not know of any prominent usages of it that way, however my knowledge is by no means exhaustive. I'd say that it's likely that the author chose that name to be かっこいい and that if any previous occurrences existed it would have been coincidence.
It's also worth mentioning that you will not find this usage in any dictionary or name kanji dictionary.