As light spills upwards into the atmosphere, it reflects off and illuminates particles of dust and liquid in the air, causing a perpetual state of twilight above many major cities. Astronomers trying to see the stars through this fog of light find it difficult to identify constellations which, in textbooks, are described as shining brightly. Another pressing concern is the ecological damage being done by unprotected light sources. Migrating animals are at risk of being disorientated and confused by excessive lighting. Birds in particular have been reported flying around, or directly into, brightly lit structures causing unnecessary death. Light at night can also interrupt the body’s circadian rhythm; an internal mechanism which controls a host of internal bodily functions. By exposing the eyes to light during sleep the brain is tricked into believing it is daytime and slows the production of melatonin, a compound believed to suppress the division of cancer. The US wastes $6 billion dollars a year on energy, which serves only to create light pollution. The fossil fuels burned to accomplish this contribute to the changing climate of the planet. The physical design of bulbs and fittings is currently being rethought with energy efficiency in mind. Shielding light fittings from sending their glow upwards into the night sky is beneficial not only to astronomers and stargazers, but to those paying the power bill. By redirecting light back towards the ground lighting engineers are significantly reducing lighting bills and cutting back on energy waste The documentary film Dark Sky looks at an isolated case of lighting design done right in the small rural town of Lake Tekapo. The measures employed at Tekapo to, protect the nearby Canterbury University Mt John Observatory from light pollution, include capping all outdoor lighting, and maintaining a lighting curfew in the surrounding region. Reducing light wastage increases energy efficiency, protects the health of animals and humans, and conserves a natural, dark night sky; for these reasons, responsible lighting should be encouraged in cities and towns within New Zealand, and around the world.