Photo by Doug Welch
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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.

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.

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.
Sky Quality Meter - LU-DL "You've got to kick at the brightness 'til it bleeds starlight."
- with apologies to Bruce Cockburn
Sky Quality Meter-LU-DL

A USB enabled data-logging light meter for night-time sky brightness monitoring!

An affordable meter for continual, connected or autonomous data-logging to measure sky brightness for astronomers and light pollution investigators.

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

Designed by Dr. Doug Welch and Anthony Tekatch

  • Measuring the night sky brightness during remote biological field experiments.
  • 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.

SQM-LU-DL control panel


  • 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.
  • Size 5.5 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:
  • SQM-LU-DL unit
  • SQM-LU-DL users manual
  • CD with PDF manual and example software
  • 15ft USB cable
  • Battery-to-USB adapter with 6 AA cells and battery holder
  • Calibration sheet indicates unit USB serial number, and calibration values
Ready to buy?

Price $249.99US plus Shipping & Handling.


What you get (with housing):
  • SQM-LU-DL unit
  • SQM-LU-DL users manual
  • CD with PDF manual and example software
  • 15ft USB cable
  • Battery-to-USB adapter with 6 AA cells and battery holder
  • Calibration sheet indicates unit USB serial number, and calibration values
  • Weatherproof housing
Ready to buy?

Price $289.94US 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-LU-DL tripod adaptor option


This adaptor kit was designed specifically for the SQM-LU-DL meter which is longer than our other meters.

The adaptor screws into the back of the SQM-LU-DL 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.

Note: The built in compass on the SQM-LU-DL-V (Vector meter) is very sensitive to hard and soft iron. You may notice variations in the Azimuth (compass reading) while mounted to a metal tripod. Also, brass screws (that come with the SQM-LU-DL-V-battery holder) must be used to secure the adaptor to the SQM-LU-DL-V.


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.