Light scattering type smoke detector

Claim 1

In a smoke detector of the light scattering type for actuating a warning device and comprising a housing containing a light source for emitting incident light having a wave length λ, a light receiving element, and a smoke collecting region so arranged that incident light from said source which contacts a smoke particle in said region is scattered such that the scattered light directed toward said receiving element forms an angle θ with the direction of the incident light, the ratio of the intensity I s of the scattered light to the intensity I o of the incident light defining an intensity ratio I s /I o for the smoke; the ratio of the intensity ratio for a black smoke to the intensity ratio for a white smoke defining the sensitivity ratio of the detector; the improvement wherein said wave length λ and said angle θ each bear a relationship to the intensity ratio and are determined as a function of one another within the limits λ ≦ 950 mμ when θ ≦ 45°, θ ≦ -0.18λ + 216 when 45° ≦ θ ≦ 135°, and θ ≦ 135° when λ = 450 mμ, to define a preselected range of sensitivity ratios for the detector.