# Twilight Sentinel

Twilight Sentinel is an automatic headlight control system developed by General Motors (GM) for use in their vehicles. The system uses a photoelectric cell to sense outside light conditions and automatically control the vehicle's exterior lights.

## History and development

The development of automatic headlight systems at General Motors can be traced back to the early 1950s. In 1952, GM introduced the Autronic Eye, an automatic headlight dimming system, for Oldsmobile and Cadillac models.
Twilight Sentinel, which expanded on the concept of automatic lighting control, was introduced in the mid-1960s. By 1964, it was available as a feature in Cadillac vehicles. The system was later expanded to other GM makes, becoming a popular feature across various models throughout the 1970s and beyond.

## Functionality

The Twilight Sentinel system operates based on the following principles:
1. Light sensing: A photoelectric cell, typically located in the dashboard, detects changes in ambient light conditions.
2. Automatic activation: In twilight or low-light conditions, the system automatically turns on the vehicle's exterior lights.
3. Automatic deactivation: When sufficient ambient light is detected, the system turns off the exterior lights.
4. Manual override: The system can be turned off or bypassed by manually operating the headlights.

## Technical details

The Twilight Sentinel system uses a photoelectric cell to measure ambient light levels. This cell is typically mounted on the dashboard of the vehicle. The system is designed to activate the vehicle's exterior lights when the ambient light falls below a certain threshold, typically corresponding to twilight conditions.
Some versions of the Twilight Sentinel system included a delay feature to prevent unnecessary switching due to temporary light fluctuations, such as when driving under overpasses or through tunnels.

## Integration with other systems

In some GM vehicles, the Twilight Sentinel system was integrated with other automatic features:
1. Automatic transmission integration: On some early 1990s Canadian GM cars with automatic transmissions, the headlights were integrated with the transmission system, activating when the vehicle was put into drive.
2. Windshield wiper integration: In more recent implementations, the system may be linked to the windshield wipers, automatically activating the lights when the wipers are in use to improve visibility in rainy conditions.

## Similar systems by other manufacturers

Other automotive manufacturers have developed similar automatic headlight systems:
1. Ford Motor Company: Ford engineers combined the features of their automatic headlight dimmer system with a Twilight Sentinel-like function, creating a comprehensive automatic lighting control system.

## Impact on automotive safety

The development of automatic headlight systems like Twilight Sentinel has contributed to improved road safety. These systems ensure that vehicles have proper illumination in low-light conditions, reducing the risk of accidents caused by reduced visibility. As automotive lighting technology continues to advance, features like Twilight Sentinel remain an important part of vehicle safety systems.