Which component is critical for determining film's reaction to light exposure?

The critical component for determining a film's reaction to light exposure is silver halide crystals. These crystals are light-sensitive compounds embedded within the film emulsion. When the film is exposed to light, the silver halide crystals undergo a chemical change, leading to the development of the image during the photographic process. The extent of this reaction is what captures the light information, ultimately resulting in a visible photograph after the development process.

Understanding the role of silver halide crystals is fundamental to analog photography, as they are responsible for the film's ability to record images based on varying light intensities. This makes them central to the way film photography operates, influencing factors such as exposure times, sensitivity ratings (ISO), and image quality derived from exposure levels. The other components listed, while important in the overall process of photography, do not directly define the film's light sensitivity or response to exposure as the silver halide crystals do.