Controlling Light Pollution

Astronomers are excited by the potential of new lighting technology to provide energy-efficient well-controlled outdoor illumination.  The dark night sky is the portal to information about planets, stars, galaxies, the early Universe, and mankind’s relation to the cosmos. Protection and enhancement of that portal serves us as professionals and as members of the family of man.

The IAU is the international astronomical organisation that brings together more than 10 000 professional astronomers from almost 100 countries. For outdoor lighting, we have two charges:

A.  Protect our gateways to the cosmos by reducing the impact of stray light on professional observatories as much as possible.
B.  IAU passed a resolution in 2009 affirming that access to a dark night sky is a universal human right, making quality outdoor lighting a worldwide imperative.

For this to be achieved three main technical priorities for controlling the nightscape have been determined and throughout the many light pollution awareness campaigns around the world are currently being implemented:


A. Use full cut-off fixtures

Light emitted immediately above horizontal has the most impact on observatories somewhat distant from urban areas; light emitted above horizontal to vertical is wasted energy and creates blinding glare from the light dome above an urban area.


B. Spectral management

Blue light scatters immediately and a mismatch to human eye sensitivity at the level at which artificial outdoor lighting is applied.

Red light has the longest legs for direct propagation, creating artificial sky glow at the greatest distances.

Strong preference for amber, with the narrowest possible energy range, consistent with requirements for colour rendition.


C. Intensity and time of use matched to application

Light intensity matched to zone - urban commercial very different from rural.  In all but the largest urban areas, little to no activity from 2:00 AM to sunrise - outdoor lighting and advertising can be greatly curtailed.  Motion activation, even on highways is a promising future direction.


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