Light Scattering

In a smoke detector, light scattering is the method of identifying suspended particles of combustion (smoke) by measuring the redirection and dispersion of a light beam when it encounters physical obstacles (particulates). Unlike obscuration, which monitors the reduction of a projected light beam, scattering principles rely on detecting light that has deviated from its original path. Specific optical variations within this category include reflection (backward/side scattering) and refraction (forward scattering).

When smoke enters this chamber, the suspended particulates intercept the light beam, causing the electromagnetic waves to scatter in multiple directions based on the particles' size, shape, and refractive index. This dispersion redirects a portion of the luminous flux toward the off-axis receiver. This sudden introduction of stray light causes a corresponding spike in the photodiode's current output.