Why not follow the more official conventions? Underscores are rarely used in Lua.
'Cause it's really hard to distinguish words with no separators and is a bad convention. It's not that bad in the standard library cause there's very few functions that are more than one word in length, but once you start writing more code it's terrible. I don't know of many lua libraries that are bigger than a few hundred lines that follow that convention. Most libraries i've dealt with use either snake_case, lowerCamel or UpperCamel.