A. Semiconductor Principle - combustion gases cause electrical charge in the semiconductor. B. Catalytic Element Principle - A material that causes accelerated combustion with increased temperature rise in a measuring element. Sees glowing embers, coals or flames. View may not be blocked or effectiveness is diminished since it then depends on reflections only. Can be confined to specific frequency range or total.
Sunlight can interfere with total detector s effectiveness.
Not sensitive to sunlight or artificial light. For complete coverage detectors should be installed throughout building. Check all space features to determine location of detectors. Highly technical matter which requires NFPA 72E to determine appropriate location considerations due to structure and type of detector. So, if the fire is small, alarms are sounded, but extinguishing is not activated unless fire gets much larger, until various hand extinguishing methods have been used to reduce damage from smoke or fire.