* Cost and Complexity: Heating an entire windscreen requires significantly more heating elements than a rear window, making it much more expensive to manufacture and install. The larger surface area also increases energy consumption.
* Visibility: While heating elements on the rear window are relatively thin and don't significantly impair visibility, embedding enough heating elements in a windscreen to effectively de-ice or defog it might compromise the clarity and optical quality of the glass, potentially affecting driver vision.
* Structural Integrity: The windscreen plays a vital role in the structural integrity of the car's safety cage. Adding numerous heating elements could weaken the windscreen, compromising its ability to protect occupants in an accident.
* Alternative Solutions: Modern cars often rely on efficient defroster systems that direct heated air from the ventilation system onto the windscreen, effectively clearing it of fog and ice. This is generally considered a more efficient and less expensive approach than directly heating the glass itself.
* Heat Dissipation: A large heated windscreen would take a long time to heat up and would also be more difficult to control evenly, leading to potential hot spots.
In short, while technologically feasible, the cost, complexity, potential impact on visibility and structural integrity, and the availability of effective alternative solutions make heating the entire windscreen impractical for most vehicles. However, some high-end vehicles *do* offer heated sections of the windscreen, typically in the wiper area, to improve clearing in extreme conditions.
