Everything from termite wings to mouse droppings can be found in a ceiling light shield. The lighted area serves as a monitoring device. By inspecting what is in the light shield during routing cleaning, you can discover if you have a pest problem. If you do suspect a problem save the crud from the light shield to show to your pest control professional for identification.

Photos of Mercure Farnham Bush Hotel, Farnham
This photo of Mercure Farnham Bush Hotel is courtesy of TripAdvisor