Re: Sky Quality Meter - first impressions

wonnerful a wonnerful.

The Lemon Sisters



Tim Killian wrote:

> 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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