How does the sweep speed affect the OSA measurements?

This is the speed at which the OSA completes a wavelength sweep (typically specified for measurement over a 100nm span). The sweep speed is especially important when performing many repetitive measurements.
 
1x setting:
This is the instrument's standard sweep speed. To meet the instrument's specifications, set the sweep speed to this value. With the sweep speed set to this value, the instrument can measure light sources ranging from line spectrum (such as the DFB-LD) to broadband wavelength (such as LEDs) light sources.
 
2x setting:
Select this value to set the sweep speed to approximately twice the speed of the 1x value. Select this value when you are measuring light sources that have comparatively gentle spectrum shape level changes, such as LED light sources.
Measurements using this value have the following characteristics:
• If you select this value when “UNCAL” is displayed, for waveforms that have sharp spectrum shape changes, such as those produced by the DFB-LD, the level and wavelength measurement accuracies may be lower than those when you select 1x. First check the measurement spectrum, and then select this value if appropriate.
• The noise level is approximately 2 dB higher than that when you select 1x.