What is the primary function of windshield heat on the 737-800?

The primary function of windshield heat on the 737-800 is to prevent ice accumulation. During flight, especially at high altitudes where temperatures drop significantly, the risk of ice formation on the windshield increases. Ice can obstruct a pilot's view and jeopardize flight safety. By applying heat to the windshield, it maintains a temperature that prevents ice from forming, ensuring clear visibility for the pilots. This is crucial for effective navigation and safe operation of the aircraft, particularly in adverse weather conditions.

The other options, while they may touch upon related aspects of flight safety or performance, do not accurately reflect the primary function of the windshield heat system. For example, while improving visibility in rain is beneficial, the main purpose of the heating element is directly related to preventing ice accumulation. The enhancement of aerodynamic performance and protection from lightning strikes are not relevant to the specific function of windshield heating. Thus, option B correctly identifies the most critical role of the windshield heat on the 737-800.