Effect of a single floodlamp in a natural area

Updated May 4, 2015

Zoltán Kolláth took these amazing images of the shadow a church tower cast on the clouds in Torniella, Italy:

Floodlit church shadow by Zoltán Kolláth is licensed under
a Creative Commons Attribution 4.0 International License.

Fisheye church shadow by Zoltán Kolláth is licensed under
a Creative Commons Attribution 4.0 International License.

The church tower is lit by a single poorly directed floodlight that shines much of the light into the sky rather than onto the tower. It dramatically demonstrates the effect that individual poorly directed lamps can have on the night environment in a natural area.

The village had turned off the public street lighting for a light pollution measurement campaign organized by the Loss of the Night Network, so we were able to compare the effect from that single lamp to the villages streetlights (which are mostly well directed). At our measurement location on a football pitch 250 meters from the church, the single lamp produced about 5% as much skyglow as the entire town's ~100 street lights put together! Keep in mind that since we can see the shadow the church projects on the sky, we're not actually under the beam of light - in other areas the effect is likely even larger.

The floodlit tower from closer up

The single floodlight that causes the problem

Whenever floodlighting is directed upward and only a portion of it hits the intended target, the rest of the light is simply wasted in brightening the night sky. However, you usually aren't able to see it because of all of the other wasted light shining into the sky. We were only able to take such an image because the village was kind enough to turn off all of the entire public lighting system for several hours each night during our measurement campaign:

The official announcement that streetlights would be turned off, displayed in a local bar

The church tower in the example above is at least an attractive element in the city. This evening in Florence we happened to notice an upward directed floodlight that was "needed" to illuminate a boring brick hotel wall. For a brief moment, we introduced a bit of darkness to make it a bit more interesting:

Light shone into the sky isn't just a waste of money and energy, it destroys one of Earth's most threatened habitats: the night. If you want to help bring the night back to Earth, consider making a donation or becoming a member of the International Dark-Sky Association.

Update 2014/05/04:

Costas Bouroussis shared these two additional images for the village with the church tower lit and off:

Torniella church light on by Costas Bouroussis is licensed under
a Creative Commons Attribution 4.0 International License.

Torniella church light off by Costas Bouroussis is licensed under
a Creative Commons Attribution 4.0 International License.

Costas also produced this time-lapse video where you can see the shadow of the church on the clouds. The three circles show approximately what a Sky Quality Meter would have reported at each of the zenith angles.

Note for new visitors: This blog is about the Loss of the Night app project, in which citizen scientists to track how skyglow is changing worldwide with the introduction of LED lights. I also have a photo series in which I profile good and bad lighting.