Which detector is sensitive to light from a flame but not to fluorescent or incandescent lighting?

• A. Photoelectric cell devices
• B. Inconel loop
• C. Pneumatic principle
• D. Optic detectors

Answer: (D)

Flame light has a distinctive spectral signature, especially in the ultraviolet region, and fires flicker rapidly as they burn. Optical detectors are built to be sensitive to that flame-specific light while using filters or sensors that ignore most ambient lighting in the visible spectrum. Fluorescent and incandescent lights emit mostly visible light and do not produce the flame’s UV signature in a way that these detectors pick up, so they stay quiet in normal lighting. A photoelectric cell is a general light sensor and would tend to respond to ambient room lighting, making it less selective for flame detection. The other two options aren’t flame-light detectors—an Inconel loop is a heating element, and a pneumatic principle relies on pressure changes rather than light.