Shingi kept testing LIGHT FORM and was glad that he had decided to turn his hand and not his entire body. Even if the transition now was almost instantaneous.
Shingi knew that it would affect his mental power the moment he turned his head into the LIGHT FROM, but it didn't affect him that much until now. But if he wasn't careful, there was even the chance of him not being able to focus enough to change back to his normal form.
The Spell was one of the few that didn't need him to keep feeding him more mana while it was active, but he needed to spend mana when he wanted to move with his new form. So, in theory, he could stay in that form indefinitely as long as he had enough MP or stayed still.
The disadvantage of that form was that the moment he entered it, even partially, his Passive Skills were inactive. That meant his MP wasn't regenerating, so it reduced the time he could keep it active.