Seeing dark skies

How we see the night sky has dramatically changed over the last century. As we move towards LED lighting for illuminating our streets, there is a changing atmosphere of our nocturnal landscapes. In 2012 Los Angeles began the move towards LED, as the city began retrofitting 141,089 street lights. The LA streetscape went from the warm orange glow of the existing high-pressure sodium (HPS) street lamps to the cool blue illumination of our LED future.

Justin Gerdes wrote for Forbes that the changeover would see an estimated $7 million in electricity savings and $2.5 million avoided in maintenance costs. Forbes also makes mention of the cost of LED fixtures going down from $432 a piece in 2009 to $245 by the end of 2012. In addition there is an increased output of 81 lumens per watt, in contrast to the 42 lumens from the HPS fixtures. With an increased life expectancy from 80,000 to 150,000 hours, in other words 17 years of life (if the lamps were to run constantly); making an LED solution the economically and environmentally superior option.

On the flip side, we are increasingly finding ourselves in a perpetual daylight, where the sky is never truly dark. As illumination technologies advance, our hours of activity blur between the less-defined distinctions of day and night. The colour of light that illuminates our night does more than give us a reference for dating the city by the street lights currently in use. It also has an effect on our secretion of melatonin; a hormone that influences our circadian rhythms (our 24 hour cycle which responds primarily to light and darkness). Blue wavelengths of light are beneficial during the daylight hours as they increase our attention and reaction times. The increase in luminosity for our cities means a diminishing connection to our dark skies. Taken in May 2014, a mosaic of NASA’s satellite images offers an incredible view of the Earth’s surface at night, where even small villages can be seen from their light source. With the increasingly bright surface of our landscape, we are becoming further removed from the stars in our sky as light pollution obscures our view.

The British Astronomical Association conducted a star count consensus between Wednesday 26th February and Saturday the 8th March 2014, asking participants to count the number of stars seen within the four corner points of the Orion constellation. Seeing more than 30 stars within Orion equated to having truly dark skies and fewer than 10 stars indicated severe light pollution. The annual survey revealed that light pollution, even in rural areas, had risen from previous years. Over half of the 1,000 people who took part in the star count could see ten stars or fewer.

As a society, our relationship to the night sky has evolved from using the stars as a tool for navigation to providing our own means of navigation around obstacles with light. With the expectation that human culture is moving in the direction of light, the question is how we can have the best of both worlds? Is colouring our light and taking advantage of LED longevity the key?

(Earth lights image from NASA)