"A ball which passes OVER a fitting attached to the ceiling, such as a light or fan, remains in play. However, a ball which passes THROUGH such a fitting is out."*

• Rules of World Singles Squash
• Abbreviated Rules
• What to do when someone asks you for a let

All of the above information is courtesy of the official site of the World Squash Federation.

http://www.worldsquash.org/ws/wp-content/uploads/2010/12/101102_Singles-Rules-V5.pdf