Netels smoke meter is based on the principle of absorption of light, which is indicative of the quality of smoke. A green LED driven by a pulsating constant current source emits a light beam having a peak spectral intensity of between 550 - 570nm. The beam passes through a smoke cell and onto a silicon photodetector, which continuously senses the intensity of light incident on it, and converts it to an electrical signal, which is further processed by precise signal handling circuits. This all solid state design ensures high stability. The output of this stage is given to a microprocessor for further processing to convert it in to suitable units including percentage opacity and absorption coefficient (K)