Unihedron Sky Quality Meter with Lens (SQM-L)

Unihedron Sky Quality Meter with Lens (SQM-L)
Item # UH-SQM-L
  • The Unihedron Quality Sky Meter L includes a built-in lens that looks at a more narrow angle of sky than the standard version, keeping ambient light from nearby buildings from disrupting your readings.
  • Just how good are the skies at your observing site? Are some times better than others? Are you fighting light pollution in your community and need ammunition?
  • Find out the answers to these questions and more with the Unihedron Sky Quality Meter-L!
  • The Unihedron SQM-L measures the brightness of the sky in magnitudes per square arcsecond.
  • The Half Width Half Maximum (HWHM) of the angular sensitivity is ~10. The Full Width Half Maximum (FWHM) is then ~20.
  • CCD users can make a correlation between the Unihedron SQM-L reading and when the background reaches some ADC level.
  • Runs on a 9V battery, included.


Finally, an affordable meter for measuring sky brightness!

The Unihedron "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 Unihedron SQM-L 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.

Specifications for the Sky Quality Meter-L...

  • 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.

  • Operates from 9V battery (included).

  • Size: 3.6" x 2.6" x 1.1"

  • Maximum light sampling time: 80 seconds

  • Specifications are subject to change without notice.

Additional Information

Additional Information

Manufacturer Unihedron
Warranty 1 Year Warranty

Customer Reviews 1 item(s)

Terrific stand alone sky quality meter!
I presently own the original one, but seeing this one had the lens that enables a much more narrow portion of the sky to be gauged, I bought this one as well. During a recent vacation in west Texas, with a stopover in Fort Davis, Texas, home of the Texas Star Party, I brought both along. Finding an area in town in the shadows afforded me the ability to to run a comparison test. I measured with the old one, and obtained a reading of 20.43. With the lens unit, I was able to record a reading of 21.63, almost a full unit of measurement darker. I know there are apps to use on a smart phone, however after owning one of these for a number of years, I feel more confident that this gives much more accurate results. My intention is to use it at home here in NJ (very light polluted skies) each night during cloud-free, no moon nights and see how the sky changes from night to night, season to season. I would highly recommend this meter.
1= Houston, We Have a Problem & 5= It's Out of This World
Review by Starman in NJ / (Posted on 1/12/2015)
Questions & Answers

Product Questions

Is it possible to measure the brightness of the Aurora by this device?
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