What feature allows a lensatic compass to function well at night?

A lensatic compass is designed for navigation in various conditions, including low-light environments. The feature that enables it to function effectively at night is the presence of luminous dials and needles. This illumination allows users to read the compass easily in the dark, ensuring accurate bearings without the need for additional light sources that could compromise stealth or visibility to others.

Luminous materials, often made from substances like phosphorescent paint, absorb light during the day and emit a glow in the dark, making the critical components of the compass visible. This distinct functionality is vital for military operations or outdoor navigation after sunset, facilitating quick and efficient navigation without losing situational awareness.

In contrast, while features like waterproofing and infrared technology enhance the compass's durability and functionality, they do not address nighttime visibility specifically. A built-in flashlight would be helpful, but it’s not a standard feature of all lensatic compasses, thus making the luminous dials and needles the essential trait for nighttime use.