Due to light pollution the night sky over many of our cities is hundreds of times brighter than a natural starlit sky.
Light pollution meter.
Light pollution map for ios showing the pollution in the north part of western europe where i live.
Thus safe currently recommends an sec of two to three watts per meter for roads less than ten metres.
The larger the number read on the meter display the darker the sky.
The graph below shows data collected in a windowless room in the apogee building using an sq 640 light pollution sensor and an at 100 µcache bluetooth datalogger the light pollution sensor was placed in the back of the room about 25 feet 8 m from the door.
It is exacerbated by excessive misdirected or obtrusive use of light but even carefully used light fundamentally alters natural conditions.
Handheld and pc based monitoring sky brightness in one meter.
Light pollution is the presence of anthropogenic and artificial light in the night environment.
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The introduction of the sky quality meter and the international year of astronomy lightmeter have led to a large number of permanent online skyglow monitoring stations.
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A meter reading of 21 00 would indicate a very dark site while a reading of 16 00 would indicate a light polluted sky.
The meter then converts that amount of light into units of magnitudes per square arc second.
For ios there is a nice app called dark sqm meter that allows you to use your phone as an sqm device to measure the darkness of your sky.
Light pollution meter pro.