Troubleshooting
After I push the button, no reading is
displayed.
Are you in a very dark location?
Yes → The Sky Quality Meter may
take up to a minute to acquire a
reading when the sky is very dark. If
your meter is operating properly, you
will here a soft beeping sound while
the measurement is in progress.
When complete, the sky brightness
will be displayed for a fixed number
of seconds.
No → Your 9V battery may need to be
replaced.
OR
The connector to your 9V battery may
be loose.
If, after you have checked for both of
these possibilities and your SQM still
won't display a reading under normal
operating conditions, contact
Unihedron for further information
and a possible replacement.
I don't know how to make sure the SQM
is off.
The SQM functions in such a way that
it is only temporarily on and turns
itself off automatically. This is a
design feature to maximize battery
life.
The readings don't repeat exactly.
Are you pointing the SQM in the same
direction each time? Under dark
conditions, you must keep the SQM
pointed in the same direction until the
reading appears on the LED display.
Your SQM must be pointed at an
altitude greater than 40 degrees above
the horizon or you may detect light
directly from surface light sources
(cars, buildings, streetlights). It is
normally the zenith sky brightness
which is measured.
The readings do not change when
pointing to various parts of the night sky.
Each SQM reading must be initiated by
pressing the button. The displayed
reading will stay on for 10 seconds
before shutting down. After the unit
has shut down, press the button to
initiate another reading.
The readings are lower (brighter) than
expected.
Make sure that no stray light from
street lights or other sources is getting
into the sensor, the sensor has a full-
angle response of 120°.
Also, check that the IR filter is in place.
This light blue glass can be seen from
the display side. A missing filter will
reveal the clear sensor.
When I use the meter during the day, all I
see is a
on the display.
The SQM has a fantastically large
range over which it will report accurate
sky brightnesses. However, to be
sensitive in the darkest conditions, it is
necessary to sacrifice the ability to
record daytime sky surface
brightnesses. Normal lux meters can
be used in such circumstances once the
effective solid angle for the lux meter's
sensor is known. The
indicates
that the sensor is saturated.
All I see is a
on the display.
The
indicates that the sensor
was unable to produce a reading. This
can occur in a light-tight dark room or
if the sensor is faulty.
Sometimes the first reading is different.
As the temperature of the unit changes
slightly due to being powered up, the
very first reading may be slightly
higher than the following readings.
Ignore this first reading and average
the following ones for the most
accurate value.
Other scales
To convert the SQM mag/arcsec² reading
to cd/m², use the following formula:
[cd/m
2
] = 10.8×10
4
× 10
(-0.4*[mag/arcsec2])
Unanswered Questions
Help us to inform you and other
customers better by forwarding
unanswered questions about the SQM and
measuring light pollution to:
Further Information
Check the Unihedron.com website for
updates and additional information.
Mailing List
Join the SQM mailing list for notifications
and to share experiences with other users
by sending an e-mail to:
sqm
✳ ✵ ✳
Contact Information
Unihedron
4 Lawrence Ave
Grimsby, ON L3M 2L9
Canada
Tel: (905) 945-1197
✳ ✵ ✳
Unihedron is a proud member of the
International Dark-Sky Association
(
www.ida.org
) and supports its goals.
Please consider joining to help preserve
the beauty of the night sky for future
generations.
✳ ✵ ✳
Warranty
Unihedron warrants this product 1 year.
✳ ✵ ✳
Last updated: September 9, 2012
