Actually there is actually a reason that rad lightning works, see it's full name is Raikô: Red Lightning, aikô is the Japanese name for Mercury Fulminate (properly known as Mercury(II) fulminate), which is a lesser explosive that was originally used to ignite gunpowder in older firearms. So in chemistry terms, the lightning wouldn't have hurt Wahl, however an ignition caused by laxus's punch would have created an explosion big enough to destroy wahl. Now I don't know why wahl couldn't scan it.
I actually didn’t know this! Cool B)