What does a bolometer primarily detect?

A bolometer is a device specifically designed to measure the power of incident electromagnetic radiation, most efficiently in the infrared range. Its operation is based on changes in thermal properties of a material when it absorbs radiation, thus enabling the detection of variations in infrared energy. This sensitivity to thermal changes makes bolometers particularly effective for detecting infrared radiation, as they can quantify the energy absorbed as heat generated within the sensor material.

The other options pertain to different ranges of the electromagnetic spectrum that are not the primary focus of bolometer technology. Visible light, ultraviolet light, and gamma rays are better detected by other types of sensors specifically designed for those wavelengths. Therefore, the correct answer is that a bolometer primarily detects infrared radiation.