The function of a removable IR filter in day/night cameras is primarily to:

The primary role of a removable IR filter in day/night cameras is to facilitate night vision. During the daytime, these cameras use an IR filter to block infrared light, allowing them to capture true color images. This results in better color accuracy under normal lighting conditions. However, at night or in low-light situations, the IR filter is removed to allow infrared light to enter the camera, which enhances the camera's ability to capture images in darkness. In this mode, the camera can utilize infrared illumination, often emitted by external IR light sources, to produce clear images even when visible light is scarce.

The other options do not directly relate to the function of the IR filter in day/night cameras. For instance, while daytime color accuracy is important, it is specifically the role of the IR filter to help the camera achieve this during the day by blocking infrared light, not enhancing battery life or increasing zoom capabilities. The intention of the IR filter is closely tied to the transition between day and night functions, making its role in facilitating night vision essential.