Invisibility depended on being able to avoid detection. Starting to throw around lightning was going to give away his position. But something with a larger area of effect would be useful.
After this particular ability had been the cause of so much trouble, Peter had sworn to control it. And he had. Radiation was far more deadly than anyone would have liked to know. A pulse of nuclear energy, one small enough to burn bright enough to hurt these shadows. It didn't take long to feel the pulse of power. Peter could see his own hands glowing. Before it could build too far, he flared off the pulse, a burst of white hot light bursting out of him. For an instant he was outlined by the glow of the flare, before it rushed away, light and heat tearing at anything in a thirty foot radius.