Extraneous light is the light from the sources (e.g light from external lamps, heated burner wall, heated boiler tubes, diffused sunlight etc.) other than the burner of the boiler. The flame detector of the burner should detect only the flame that is emitted from the burner, not from other sources. The dynamic behavior of the burner flame is used to differentiate the extraneous light flame from the burner flame.
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