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This paper provides the initial steps in the overall design and implementation of a control system that utilizes optical sensors to monitor individual burners in a furnace system. The key component of such a system is the optical sensor, which produces a signal that corresponds to the air-to-fuel ratio for the given flame. A single propane or natural gas fueled flame was monitored with a single optical sensor responsive to emission wavelengths between approximately 350 to 1100 nm. Air or fuel flow was controlled in order to shift the air/fuel ratio from fuel-lean to fuel-rich and back to fuel-lean. Results show that when the optical sensor was correctly positioned its normalized output voltage had a pronounced peak value that occurred very close to the stoichiometric air/fuel ratio. The normalized response decreased by approximately 30% at equivalence ratios of 0.8 and 1.25.