What type of energy do spark/ember detectors specifically react to?

Spark/ember detectors are specifically designed to respond to radiant energy from embers. These detectors utilize sensors that can detect the heat emitted by glowing embers or sparks, which is often referred to as radiant energy. The technology in these detectors is fine-tuned to recognize the specific wavelengths of energy that are indicative of burning embers, allowing them to sense the early signs of fire.

The reason this focus is important is that embers can travel through the air and ignite other materials, making early detection critical for fire prevention. By specifically tuning to radiant energy from embers, these detectors can provide an advanced level of fire safety.

The other options are not correct primarily because they do not focus specifically on the detection of embers. While thermal energy is associated with heat, it is broader and includes all heat sources, not just embers. Radiant energy from flames would pertain to flames rather than the glowing embers left behind when something burns. Ultrasonic waves do not relate to the detection of fire or embers but instead pertain to sound frequencies beyond human hearing, which are not applicable in fire detection.