Laser particle counters work on the principal of light scattering or light blocking. The air enters through an isokinetic sampling probe and through a chamber inside of the particle counter. A Laser beem illuminates the particles and light is redirected or absorbed. Light that comes in contact with particle is scattered in specific directions in relation to the original direction has a unique signature which relates to the size of the particle and allows the particle counter to determine the size and quantity of individual particles.