Which of the following is NOT a type of small unit illumination?

The concept of small unit illumination refers to methods used to enhance visibility on the battlefield during night operations or in low-light conditions, often for tactical advantages.

Among the various options, ground pop-up devices, trip flares, and grenades are all types of illumination used to assist troops in seeing the terrain or enemy movements, either by emitting light or providing a visual cue. Ground pop-up devices provide immediate area lighting by releasing a bright light when triggered. Trip flares function similarly, igniting when disturbed to alert personnel and illuminate the surrounding area.

In contrast, a signal flare specifically serves primary purposes of signaling and communication rather than providing local illumination for a small unit. While a signal flare indeed emits light, its main function is distinct from that of illumination tactics, as it is primarily used to attract attention or convey a specific message to distant forces rather than illuminate a specific area for immediate tactical engagement.

Thus, the identification of signal flare as the option that does not fit with the other types of small unit illumination is based on its distinct purpose serving communication needs instead of tactical illumination for nearby operational support.