Twilight monitoring using the SQM

There may be cases where it is desirable to measure light levels in the transition between night and day. The SQM products are very sensitive to night light, but will saturate in the daylight.

Our meters are mostly used to give an idea of sky brightness at the zenith and are too sensitive to give defined readings once the Sun has risen. For this reason, we have designed an adaptor to hold a Neutral Density (ND) filter to subdue the incoming light. ND filters are fairly inexpensive and are supplied at many astronomy equipment dealers.

We have a live unfiltered SQM-LE operation in Grimsby Ontario, Canada (time zone = EDT). You can see the plot here. The plot is cropped at 16mpsas. Valid readings continue up to about 8mpsas and more detail about twilight could be extracted from there. You will be able to see the available resolution that an unfiltered SQM-L series meter provides around dawn/dusk.



SQM Resources

External resources