Both of the sources will be on, what you are looking at in the attached picture is the selection of what will be the “main” wavelength which is used for the DFT results for the observation lines and observation planes. So if you have a source at 1.55 and one at 2 but select 1.55 both sources will be on but when observing the DFTs in Analyzer you will only be able to see DFT based on 1.55. Observation points have the full time information so you can recalculate the DFT for whatever range you want.