Some cars have quarter light glass which is a small, separate side window in either the front door, directly in front of the main car window, or situated on the sides of the car just in front of the rear windows of the car, in the 'C-pillar'.

quarter light glass is situated on the door. Quarter light glass is often triangular in shape but can be come in various shapes depending on the make, model and year of car. This window can be hinged, enabling it to open inwards, and is sometimes referred to as a vent window, allowing a small amount of air in, to ventilate the car. Quarter light glass on some cars may, instead, be fixed in place, forming a side window that doesn't open.

Glass used in modern car doors is generally safety glass which decreases the chance of injury if it smashes.

All of the windows in the car serve a safety function, offering protection to the people travelling in the car. All windows should be clean and free from cracks and scratches so that safety is not compromised. All window parts and mechanisms should be functioning fully in order to be able to perform properly and safely. If the quarter light glass has been smashed or cracked, as a result of an accident, for example, it's vital to replace this part as soon as possible. When replacing the windows in your car it's important that they fit perfectly. Buying the quarter light glass, will ensure the window is compatible with the make and model of your car.