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Latest News

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.

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.

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
Earth Hour plot Rick Wagner reports on his Earth Hour findings
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.
Downloads of users contributions.
Database of Sky Quality Meter readings from around the world.
Sky Quality Meter - L "You've got to kick at the brightness 'til it bleeds starlight."
- with apologies to Bruce Cockburn
Sky Quality Meter-L

An affordable meter for measuring sky brightness for astronomers!

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

Unprecedented sensitivity in a handheld meter!

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.


  • Audible signal while measurement is in progress.
  • Sky brightness displayed in visual magnitudes per square arcsecond.
  • Infrared blocking filter restricts measurement to visual bandpass.
  • Temperature in both Celsius and Fahrenheit as well as model number and serial number can be displayed with different button press sequence.
  • Precision readings at even the darkest sites.
  • Power-saving features designed in for maximum battery life.
  • Reverse battery protection.

  • 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. Comparison chart.
  • Operates from 9V battery (included).
  • Size 3.6 x 2.6 x 1.1 in. (92 x 67 x 28mm)
  • Maximum light sampling time: 80 seconds.
  • Specifications are subject to change without notice.

Unihedron supports the goals of the International Dark-Sky Association .

Details: Reports including the SQM:
  • Night Sky Photometry with Sky Quality Meter by Pierantonio Cinzano.
  • "Contributions of artificial lighting sources on light pollution in Hong Kong measured through a night sky brightness monitoring" article by Chun Shing Jason Pun, Chu Wing So, Wai Yan Leung, Chung Fai Wong.   Science direct  arxiv.
  • Human Contrast Threshold and Astronomical Visibility paper by Andrew Crumey.
  • Report on sky colour: Red is the new black; Chris Kyba and colleagues PDF.
  • Documenting Local Night Sky Brightness report, Jennifer Birriel of MSU.
  • Measure Night Sky Brightness at Various Zenith Angles report, Jennifer Birriel of MSU.
  • "Night sky photometry and spectroscopy performed at the Vienna University Observatory" published in the "Journal of Quantitative Spectroscopy and Radiative Transfer" Science Direct  arXiv.
  • "The night sky brightness at Potsdam-Babelsberg including overcast and moonlit conditions" published in the "Journal of Quantitative Spectroscopy and Radiative Transfer" Science Direct  arXiv.
  • "Worldwide variations in artificial skyglow" by Christopher C. M. Kyba, Kai Pong Tong, and more. Published in : Scientific Reports.
  • "Intercomparisons of Nine Sky Brightness Detector" by Peter den Outer, Dorien Lolkema, Marty Haaima, Rene van der Hoff, Henk Spoelstra, and Wim Schmidt. Published in 2014 The National Center for Biotechnology Information.
  • Calibration of SQM-L photometers for the NixNox project, Zamorano Calvo, Jaime and Munoz MarĂ­n, Victor Manuel (2010),
  • Zamorano, Jaime y Munoz Marin, Victor Manuel (2010), Calibration of SQM-L photometers for the NixNox project. [ LICA report; no. #01],
  • Zamorano, Jaime & Ruiz Carmona, Roque (2013), Sky Quality Meter cross-calibration for the NixNox project. [ LICA report; no. #03],
  • Nievas Rosillo, Miguel & Zamorano, Jaime (2014), *PySQM the UCM open source software to read, plot and store data from SQM photometers*,
  • Zamorano, Jaime, Sanchez de Miguel, Alejandro, Martinez Delgado, David & Alfaro Navarro, Emilio (2011) Proyecto NixNox disfrutando de los cielos estrellados de Espana. Astronomia (142). pp. 36-42. ISSN 1699-7751,
  • Zamorano, Jaime, Sanchez de Miguel, Alejandro, Nievas Rosillo, Miguel & Tapia Ayuga, Carlos (2014) NixNox procedure to build Night Sky Brightness maps from SQM photometers observations.,
  • A night sky brightness network with data obtained with fixed SQM photometers of the Spanish Light Pollution Research Network.
Light pollution maps / databases: Useful Light pollution links:

SQM-L tripod adaptor option


This adaptor kit was designed specifically for the SQM-L so that the battery compartment is accessible with the adaptor in place.

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

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

3D part view


Buy SQM-L now:
Price $134.99US plus Shipping & Handling.

You may also be interested in; our low-cost sky meter (SQM), or our Ethernet conected sky meter (SQM-LE), or our USB connected model (SQM-LU).
Compare models.
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