Sky Quality Meter - first impressions

I received a Sky Quality Meter (SQM) from Unihedron last week and have a few comments after using it several times. The SQM uses a Texas Instruments optical sensor IC to measure sky brightness in a 80-degree cone (approx. 1.5*pi steradian). The company claims the sensor is temperature compensated from -40C to +40C. Measurements are displayed in units of magnitude/sq. arcseconds.

Mechanical packaging -

The unit is housed in a black plastic case that resembles an old-style photographic light meter. The light sensor and 4-digit, red LED readout are on one end of the case. Power is supplied by a 9V battery (included) accessible through a slide-off cover. Having the display on the same end as the light sensor seemed at first like a dumb idea, but since the display is always off during a measurement, it doesn't really affect the operation of the SQM.

Operation-

A single pushbutton switch activates the meter and starts a measurement cycle. At the end of the integration period, the display illuminates and shows the reading for a few seconds, then the meter automatically turns off. For sky measurements, I typically held the meter overhead toward zenith. The integration time at my location was never more than about five seconds, and the readings were typically in the 18.5-19.7 range (not all that dark). Really dark skies might require much longer integration times (the unit beeps once per second) for a measurement. Also available for display is the local temperature (degrees C & F), the firmware revision level, and the unit serial number.

Conclusion-

The SQM is exceedingly simple to use, and IMO is priced affordably at $79. While I can't verify any of the claims for precision or absolute calibration (+/- 10% of readings), it seems it would be a useful tool for comparing sky quality even if it's only used for relative readings.

Possible improvements -

A memory function that allows display of the previous ten readings might be useful. In very dark sites, a threaded socket for tripod mounting would be handy so the unit could remain pointed in the same direction during the longer integration period.

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