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Portable instrument is able to measure light pollution in cities

16 June 2013

University of Granada researchers have patented a new portable means of measuring and quantifying the levels of light pollution in a city.

The University of Granada's 'All-Sky' portable light pollution measuring system
The University of Granada's 'All-Sky' portable light pollution measuring system

Claimed to be much more accurate and reliable than those currently used. it instantly quantifies the levels of light pollution or artificial brightness of the night sky background using a system that includes an all-sky camera and several interference filters.

The instrument is easily transported and can be used practically anywhere, without the need for large-scale installations like astronomical observatories. The researchers are currently looking for companies interested in developing and manufacturing both the instrument and the calibration and measuring procedure. Dr Ovidio Rabaza, principal researcher on the project, explains how it works:

“Our measurement technique uses the radiance emitted by any calibration lamp with a known radiant flux in the interior of an integrating sphere. The sphere's internal wall is a Lambertian surface, which ensures the light it reflects is uniformly dispersed in all directions, guaranteeing that the measurement patterns are almost perfect and, therefore, very accurate. Moreover, the multi-band measurements provide information about very narrow spectral bands that enable us to determine the type of light source". 

The image acquisition system consists of a thermo-electrically-cooled CCD camera with an internal filter wheel. The camera is also equipped with several narrow-band interference filters and a fish-eye objective, capable of taking a full-sky image in a single exposure and with each filter focused permanently to infinity. 

The researchers say that, for the first time, relative irradiance and sky background luminance have been measured through wide-field images of the sky, instead of using more conventional methods, like astronomical photometry.

Moreover, since it uses lights as calibration sources instead of standard stars with known flux — as do current classical astro-photometry methods — you don't need to know about astronomy to measure sky background brightness so, once the instrument's been calibrated, measurement is instantaneous.

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