Creates a protective magical force around the caster, faintly visible as a shimmering globe. The sphere increases the wizard's AC by 2 and also acts as a defensive sponge that soaks up damage received. The armour has 4 hit points per proficiency modifier. When any attack or effect inflicts damage on the wizard, the armour's hit points are lost first. Should an attack reduce the armour's hit points to 0, the shimmering globe collapses and any residual hit points of damage are removed from the wizard's own current hit points. Note that the shimmering globe interferes with any stealth attempts and any such checks are made with disadvantage. 

At higher levels: for every spell slot used above 3rd level, the armour has an extra 2 hit points per proficiency modifier. So if cast as a 4th slot by a 7th level wizard, the armour has 18 hit points.