Flame detectors detect __________ and __________ light spectrums.

• A. Ultraviolet / Ionization
• B. Heat / Infrared
• C. Infrared / Ionization
• D. Ultraviolet / Infrared

Answer: (D)

Flame detectors respond to radiation emitted by a flame in specific portions of the light spectrum. Two common signals they look for are ultraviolet and infrared.

Ultraviolet radiation comes from the chemiluminescence of excited flame radicals, which allows the detector to pick up a flame quickly, even when it’s small. Infrared radiation corresponds to the heat energy emitted by the burning fuel, helping the detector sense larger or hotter flames. Using both ultraviolet and infrared signals together increases reliability because they cover different flame characteristics and are less susceptible to false alarms than using one spectrum alone.

Choosing anything related to ionization isn’t appropriate here, since ionization deals with electrical changes rather than light wavelengths. Likewise, referring to heat alone isn’t a light spectrum, whereas infrared is the part of the spectrum that represents heat radiation.