Which of the following is allowed to be inside exterior light housings?

Interior light housings are critical components of a vehicle's exterior lighting system. They are designed to protect the light bulb and wiring from various external elements that could impact functionality and safety.

Moisture is allowed inside exterior light housings to a certain extent, particularly if the design includes venting to allow for condensation to escape or drainage features that avoid pooling of water. This is important because environmental factors can cause humidity and condensation buildup. Therefore, manufacturers may design housings to withstand these conditions, preventing electrical shorts or corrosion that might arise from moisture exposure.

Other options, like air, dust, and debris, can interfere with the light's performance and longevity. Dust and debris can obstruct the light emitted or scratch the lens, leading to reduced visibility. While air is not harmful per se, excessive dust particles suspended in the air can settle inside the housing and cause similar issues. Proper sealing of light housings is necessary to prevent these contaminants from entering, ensuring the light system operates efficiently and safely.