Photo by Doug Welch
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Latest News

RESEARCH ARTICLE: ENVIRONMENTAL PROTECTION The new world atlas of artificial night sky brightness by Fabio Falchi, Pierantonio Cinzano, Dan Duriscoe, Christopher C. M. Kyba, Christopher D. Elvidge, Kimberly Baugh, Boris A. Portnov, Nataliya A. Rybnikova, Riccardo Furgoni

New Brunswick, Canada: Grade 8 students Holly Ayles and Emily Baxter are national winners in the recent International Statistical Literacy Poster Competition. Their poster will go to international level in Dublin Ireland later in August.

Clear Sky Detection experiment
Here is an experiment to try to identify a clear sky using the SQM-LE/LU by observing the fluctuations in light level caused by clouds.
Details here.

A Survey of Light Pollution in Hong Kong.
Researchers at the Department of Physics of The University of Hong Kong completed their light pollution survey and collected near 2,000 night sky brightness data sets from SQMs at more than 220 observation sites around Hong Kong during the past 15 months.
Full report here.

GLOBE at Night: Shed Light on Light Pollution! Podcast. Connie Walker of the NOAO discusses the Globe at Night project as part of the 365 days of astronomy during the Year of Astronomy.

Knightware, makers of "Deep-Sky Planner", have released SQM Reader Pro for Windows and the SQM-LE. This low-cost package adds graphing, statistical calculations, extended data storage and transmission capabilities to the basic feature set of existing "SQM Reader" software.

Dark Skies Awareness, an IYA2009 cornerstone project helps people appreciate the dark sky with 11 projects including the GLOBE at Night campaign using both visual and SQM readings.
Hong Kong light pollution survey
A survey of light pollution in Hong Kong using various tools including the Sky Quality Meter
Unihedron receives the Executive Director Special Award and the Certificate of Appreciation for its exhibit at "The Night: Why Dark Hours Are So Important" symposium in Washington DC.
Sky Quality Meter - LU "You've got to kick at the brightness 'til it bleeds starlight."
- with apologies to Bruce Cockburn
Sky Quality Meter-LU

A USB SQM model for night-time sky brightness monitoring!

An affordable meter for continual, connected measuring of sky brightness for astronomers!

The "Sky Quality Meter - LU" measures the brightness of the night sky in magnitudes per square arcsecond.

Designed by Dr. Doug Welch and Anthony Tekatch

  • Find out how good the night or site REALLY is.
  • Compare the sky brightness at different sites quantitatively.
  • Document the evolution of light pollution in your area.
  • Set planetarium dome illumination to mimic the skies people are likely to experience elsewhere in the city.
  • Monitor sky brightness through the night, night-to-night, and year-to-year.
  • Determine which nights show the greatest promise for finding the 'faintest fuzzies'!
  • Calibrate the effect of sky brightness on qualitative measures such as the Bortle Scale.
  • Investigate how sky brightness correlates with the solar cycle and month-to-month sunspot activity.
  • Help provide local ground truth for future sky brightness prediction with the Clear Sky Clock.
  • CCD users can make a correlation between the SQM reading and when the background reaches some ADC level.


  • Sky brightness reported in visual magnitudes per square arcsecond.
  • Infrared blocking filter restricts measurement to visual bandpass.
  • Sensor temperature, model number, and serial number are provided.
  • Precision readings at even the darkest sites.
  • Field-upgradeable firmware.
  • Open protocol document.

  • USB connectivity
  • Included applications for reading data in Perl.
  • The Half Width Half Maximum (HWHM) of the angular sensitivity is ~10°. The Full Width Half Maximum (FWHM) is then ~20°. The sensitivity to a point source ~19° off-axis is a factor of 10 lower than on-axis. A point source ~20° and ~40° off-axis would register 3.0 and 5.0 magnitudes fainter, respectively. Annotated FOV spec.
  • Comparison chart.
  • Size 3.6 x 2.6 x 1.1 in.
  • Maximum light sampling time: 80 seconds.
  • Minimum light sampling time: 1 seconds.
  • Specifications are subject to change without notice.

What you get: Meter only
  • SQM-LU unit
  • USB flash drive containing the users manual, operation software (UDM), and example software. This can also be found online.
  • 15ft USB cable
  • Calibration sheet indicates unit USB serial number, and calibration values
Ready to buy?

Price $218US plus Shipping & Handling.


What you get: Meter and weatherproof housing
  • SQM-LU unit
  • USB flash drive containing the users manual, operation software (UDM), and example software. This can also be found online.
  • 15ft USB cable
  • Calibration sheet indicates unit USB serial number, and calibration values
  • Weatherproof housing
Ready to buy?

Price $264US plus Shipping & Handling.


Details: Software Downloads: Reports including the SQM: Light pollution maps / databases: Useful Light pollution links: USB information:
Unihedron supports the goals of the International Dark-Sky Association.

SQM tripod adaptor option

SQM example

SQM-L example

SQM-LE example

SQM-LU-DL example

This adaptor kit was designed to fit the SQM, SQM,L,LU,LE,LR,DL. The battery compartments in the handhelds meters is accessible with the adaptor in place.

The adaptor screws into the back of the meter and allows the meter to be mounted on a tripod with a 1/4-20 thread.

The kit includes one tripod adaptor, 3D-printed black or white plastic adaptor, and two longer screws (to replace two short screws already in the meter).

3D part view

SQM-x-TA Kit

Sky Quality Meter  - Window mount


This Window mounting bracket is used for moving light pollution studies while a "connected" meter and GPS are attached to a computer using UDM logging the continuously with GPS option enabled described at this forum post.

Read more details here.


You may also be interested in; the SQM-LE/LU housing, or our low-cost handheld sky meter (SQM), or our narrow-field handheld sky meter (SQM-L), or our Ethernet conected sky meter (SQM-LE).
Compare models.