This spell creates an immobile, faintly shimmering magical sphere around the caster that prevents any 1st-, 2nd-, or 3rd-level spell effects from penetrating (i.e., the area of effect of any such spells does not include the area of the minor globe of invulnerability).
This includes innate abilities and effects from devices. However, any type of spell can be cast out of the magical sphere, and these pass from the caster of the globe to their subject without affecting the minor globe. Fourth and higher level spells are not affected by the globe.
The globe can be brought down by a successful dispel magic spell. The caster can leave and return to the globe without penalty.
Note that spell effects are not actually disrupted by the globe unless cast directly through or into it: The caster would still see a mirror image created by a wizard outside the globe. If that wizard then entered the globe, the images would wink out, to reappear when the wizard exited the globe. Likewise, a wizard standing in the area of a light spell would still receive sufficient light for vision, even though that part of the light spell volume in the globe would not be luminous.
The material component of the spell is a glass or crystal bead that shatters at the expiration of the spell.