The Universe in Mind - Dr. Chris Baddiley

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Light Pollution - Introduction

I retain my passion for astronomy and dark skies.  These two items are inextricably linked, without good light design the beauty of a starry night sky is denied to everyone.  You don't need to be a phyiscist to appreciate the wonder of our starry heavens.  The World's lights at night

When the sky is truly dark then we are able to see the stars, comets and planets which have fascinated mankind for centuries. This image show Comet Hale Bop flying passed the earth in 1997.

It isn't just the beauty of the skies which is wasted when light pollution becomes a problem, all that light which is scattering through the atmosphere is failing to light the streets and roads where it is actually wanted. That is a lot of energy going to waste!
Light pollution hides the stars from us.

Thanks to BBC Hereford and Worcester

Light which comes straight up from the source goes out to the sky and doesn't cause any further problems beyond the waste of energy. Light which comes horizontally out from the light is bounced back down by the atmosphere causing the sky pollution. 
A small source at the focus of a conic section reflector with flat glass shines down in a confined cone. Some at extreme angles is reflected back in.

Luminaire Type

Upward light ratio (fraction of total above horizontal)

Ground reflection

Upward fraction including ground reflection

Standard SOX




Cut off SON




Full cut off SON




"There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened." -Douglas Adams