Light Pollution in the Near Infrared

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1 Light Pollution in the Near Infrared Ž. Andreić 1, D. Andreić 2 and K. Pavlić 1 1 Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb, Pierottijeva 6, Zagreb, Croatia zandreic@rgn.hr, kpavlic@rgn.hr 2 Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, Zagreb, Croatia. dandreic@vef.hr Osnabrueck Andreić at al: Light Pollution in the Near Infrared 1

2 Overview 1. Introduction 2. CCD and C-MOS cameras 3. visible and infrared sky 4. past and future 5. conclusions Osnabrueck Andreić at al: Light Pollution in the Near Infrared 2

3 Introduction Light pollution (LP) is usually conected to human vision, so only visible part of EM radiation (light) is considered in studies of LP. Osnabrueck Andreić at al: Light Pollution in the Near Infrared 3

4 CCD cameras are sensitive to infra-red (IR) up to 1000 nm! CCD IR and there is "LP" in this spectral region too! C-MOS Osnabrueck Andreić at al: Light Pollution in the Near Infrared 4

5 Modified DSLR camera with filters Relative spectral sensitivity UV-IR cut no filter RG Wavelength (nm) Osnabrueck Andreić at al: Light Pollution in the Near Infrared 5

6 Monitoring methods: modified DSLR + fish-eye lens + filter Light sources at the horizon can be hiden by a circular lens hood covering horizon up to 10 o altitude. blue UV-IR cut Nd and -IR 25A R72 RG830 Osnabrueck Andreić at al: Light Pollution in the Near Infrared 6

7 semi-rural sky, SQM-L: 20.2 at zenith, UV-IR cut Osnabrueck Andreić at al: Light Pollution in the Near Infrared 7

8 same sky, RG830 (IR) Osnabrueck Andreić at al: Light Pollution in the Near Infrared 8

9 Results Visible Infrared isophote each 10% % Osnabrueck Andreić at al: Light Pollution in the Near Infrared 9

Monitoring methods: modified DSLR + spectrograph - Fast prismatic spectrograph - covers 420-1100 nm - wavelength calibration lamp integrated -

10 Monitoring methods: modified DSLR + spectrograph - Fast prismatic spectrograph - covers nm - wavelength calibration lamp integrated - records natural sky spectrum in 5 min at ISO 1600 with a modified DSLR Osnabrueck Andreić at al: Light Pollution in the Near Infrared 10

11 LP spectrum, same place Ne comparison Sky spectrum around zenith Osnabrueck Andreić at al: Light Pollution in the Near Infrared 11

12 Results 1 0,9 0,8 0,7 HP Na lamps Na 818,3 nm intensity (a.u.) 0,6 0,5 0,4 0,3 0,2 0, wavelength (nm) Osnabrueck Andreić at al: Light Pollution in the Near Infrared 12

13 HP-Na bulbs are the culprit! HP-Na sky MH Osnabrueck Andreić at al: Light Pollution in the Near Infrared 13

14 possible solutions custom interference filter? 1 0,9 0,8 RG 850 0,7 intensity (a.u.) 0,6 0,5 0,4 0,3 0,2 0, H α wavelength (nm) Osnabrueck Andreić at al: Light Pollution in the Near Infrared 14

"white" LED Osnabrueck 2011 - Andreić at

15 Past and future: visible IR HP mercury HP sodium metal halide Incandescent halogen "white" LED Osnabrueck Andreić at al: Light Pollution in the Near Infrared 15

16 Conclusions 1. There is strong LP in the near infrared, and it is produced by the same sources responsible for the LP in the visible part of the spectrum. Sodium bulbs produce very strong IR LP. 2. IR is not as crowded with LP spectral lines as visible part of the spectrum, good filtering is still possible. 3. Scattering of the IR light is not as effective as for the visible light, so the IR sky quality is little better. Also, natural sky brightness is higher in the IR, making LP less prominent. 4. Light cirrus clouds are often prominent in the IR, but are invisible in the visible light. Osnabrueck Andreić at al: Light Pollution in the Near Infrared 16

17 Conclusions 2 5. New metal-halide (MH) lamps polute more than sodium HP lamps, both in the visible and in the IR. 6. LED sources polute only in the visible, but show a very worrysome excess of blue light, that should be filtered at the source at any cost. Osnabrueck Andreić at al: Light Pollution in the Near Infrared 17

18 Acknowledgements The speaker s attendance at this conference was sponsored by the Alexander von Humboldt Foundation. Osnabrueck Andreić at al: Light Pollution in the Near Infrared 18

19 Thank you for your attention! Questions? Osnabrueck Andreić at al: Light Pollution in the Near Infrared 19

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