I am putting up a security light. Will that hurt my views of the sky?
Yes! The single worst thing to happen to amateur astronomy is the increasing use of the unshielded 175-watt dusk-to-dawn mercury vapor “security light” in rural areas.
These blazing lights send a great deal of their output either sideways or up. This is a big waste, and it ruins the nighttime sky.
The International Dark-Sky Association (IDA) reports that in areas where 97% of the US population live, the sky is always at least as bright as it is when there is a half Moon at one of the world's best observatory sites. For 40% of the US population it is never dark enough at night for human eyes to become adapted to night vision. Light pollution is the reason for this. And it makes seeing something that every culture throughout human history has been able to see, study and wonder about, our own the Milky Way, impossible to see. Most children will never see this bright band of trillions of stars outside of a tv or computer screen in their lifetime.
If you must install a security light, please choose a shielded “shoebox” design where the light shines in a downward cone, but not sideways or up. In addition, install a motion sensor so it only turns on when needed. We have been on rural farms where the owner could not even turn the light off! Make sure you have a switch for this. For more information, go to the International Dark-Sky Association’s website at www.darksky.org.
