Light trespass

Description and cause
Light trespass occurs when neighbors of an illuminated space are affected by the lighting system’s inability to contain its light within the area intended.
The inappropriate selection, tilting, or aiming of outdoor luminaires for the particular lighting task causes light trespass.

Ways to minimize
Minimize light trespass through careful selection of lamp wattage, luminaire type, and placement.
Appropriate reflector selection, aiming, and shielding of the luminaires can keep the projection of the light within property boundaries.