What additional safety feature must be included with Type 1 life jackets?

Type 1 life jackets are designed for maximum buoyancy and are ideal for situations where rescue may take longer, providing a high level of safety for the wearer. An approved light and whistle are crucial additional safety features because they enhance visibility and communication in emergency situations. The light helps rescuers locate individuals in the water during low visibility conditions, such as at night or in poor weather. The whistle serves as an audible signaling device, alerting nearby boats or rescuers to the wearer's presence and location.

Including these features ensures that regardless of the circumstances, the individual wearing the life jacket has the necessary tools to signal for help effectively, thereby increasing their chances of survival until rescue is possible. Other options listed, while potentially useful, do not directly contribute to the critical safety enhancements mandated for Type 1 life jackets as effectively as the light and whistle do.