We report on a comparison of free space and Cavity-Enhanced Raman Spectroscopy (CERS) for gas phase measurements of nitrogen and oxygen in ambient air. Real time analysis capabilities, and continuous Raman signals with low power diodes, make the technique non-invasive, affordable, compact and applicable for usage in non-reacting flows. We derive a comprehensive model for estimation of photon emission for both free space and cavity based signals and discuss tradeoffs in how to organise the cavity geometry for maximum gain relatively to free space. Measurements in both free and cavity configurations are compared to the expected cavity enhancement. The present results can serve as a quick guide on how to use continuous wave low power lasers in a cavity setup to obtain enhanced laser induced Raman scattering.