Smoke detector

A smoke detector comprising:

• a casing having therein a smoke detection chamber to detect smoke;
• a first light disposed in the casing, the first light being configured to emit light having a first wavelength to the smoke detection chamber, the first light having a first emission axis;
• a second light disposed in the casing, the second light being configured to emit light having a second wavelength to the smoke detection chamber, the second wavelength being longer than the first wavelength of the first light, the second light having a second emission axis;
• and
• a light receiver disposed in the casing, the light receiver being configured to receive the light emitted from the first light and the light emitted from the second light, the light receiver having a reception axis,
• wherein a second scattering angle that is an angle between the reception axis of the light receiver and a second extension extending from an intersection of the second emission axis and the reception axis in a direction away from the second light is larger than a first scattering angle that is an angle between the reception axis of the light receiver and a first extension extending from an intersection of the first emission axis and the reception axis in a direction away from the first light,
• a controller configured to receive an intensity of scattered light received by the light receiver,
• a storage unit storing:
• a white smoke threshold value set between a grey-smoke-induced scattered light intensity, serving as a reference, and a white-smoke-induced scattered light intensity;
• and a black smoke threshold value set between the grey-smoke-induced scattered light intensity and a black-smoke-induced scattered light intensity,
• wherein the controller determines presence of white smoke when the intensity of scattered light received by the light receiver exceeds the white smoke threshold value stored in the storage unit, and determines presence of black smoke when the intensity of scattered light received by the light receiver exceeds the black smoke threshold value stored in the storage unit.