When should the brake indicator lamp turn off?

The brake indicator lamp is designed to inform the driver of an issue with the braking system or that the parking brake is engaged. The lamp should turn off when the brake is released because this indicates that the braking system is functioning normally and that the parking brake is disengaged. A properly functioning vehicle should not have the brake indicator lit when the brakes are not being actively applied, reflecting that the brakes are ready for normal operation.

In contrast, the other options do not align with the mechanical operations and safety indicators related to the braking system. For example, the vehicle's speed of 30 mph is irrelevant to the operation of the brake indicator; it should not depend on speed. The light is also not tied to whether it's day or night, nor does it relate to how long the vehicle has been parked. The critical factor is simply the engagement status of the brake.