What is the difference between the SQM and SQM-L?
Here is a chart showing the differences at a glance. The main difference is the field of view. The SQM-L (with lens) is an improvement over the SQM. The lens collects more light from a smaller cone so that the meter is not affected from lights or shading on the horizon. The SQM spec for field of view is located in this technical report. A comparison of the angular response for both meters is here. Generally speaking, the SQM-L ‘Half Width Half Maximum’ is ~10 degrees as opposed to ~42 degrees for the SQM. The SQM-L is better suited for astronomy and dark sky enthusiasts. It has a lens to narrow the field of view so that street lights and buildings or trees do not affect the reading very much. If you expect to always take readings at dark sky sites in an open field then the regular SQM will do fine for that task. Note: The SQM-LE has the same optics as the SQM-L.
