You should Select Intensity Correction when comparing sources with continuum spectra (e.g., incandescent sources).

Please note that this correction will only work properly if you are using the optical fiber attachment to your Vernier-branded spectrometer. See http://www.vernier.com/products/accessories/optical-fiber-cables/ for the correct optical fiber for your spectrometer.

DO NOT use the Intensity Correction if you are comparing emission lines from discharge tubes.