The ultraviolet viewing head is recommended for gas and oil flames. It consist of a gas discharge type sensor with a spectral response only in the UV region, approximately 185 to 300 nanometers with a peak response at 200 nanometers. The highest UV intensity occurs near the flame root (first 30% of the flame) but this zone of higher UV intensity does not overlap the same zone of adiacent or opposing burner so that, with proper sighting, discrimination is predictable.