Monday, December 8, 2014

Greenhouses at night

Last week I posted some photos showing examples of trees that seemed to be affected by the light from nearby street lamps. There hasn't been much research into what effect (if any) street light has on trees. But when it comes to higher light levels, we do know that plants respond to the light, and use it to grow.

Some greenhouses use artificial light to extend the growing time of plants beyond what is possible with local sunlight. When greenhouses don't bother to capture and redirect scattered light back towards the plants, this can have a really profound effect on the night sky. The image below was taken by my Dutch colleague Kamiel Spoelstra:

Skyglow from greenhouse by Kamiel Spoelstra is licensed under
a Creative Commons Attribution 4.0 International License.

Of the places where accurate measurements of sky brightness have been reported, the brightest skies I know of are near greenhouses in the Netherlands. When you look at satellite images of the Earth at night from the new VIIRS DNB instrument, greenhouses are "blindingly" obvious, because they are tens or even hundreds of times brighter than city centers. This is part of the reason the Netherlands appears so bright - it has a lot of greenhouses!

Northwestern Europe at night by VIIRS

My colleague Florian Tornow took the next two photos from a window on a recent flight to the Netherlands. The first shows a large area of greenhouses:

Greenhouse complex by Florian Tornow is licensed under
a Creative Commons Attribution 4.0 International License.

The second shows how bright they can be compared to the surroundings:

Lit greenhouses at night by Florian Tornow is licensed under
a Creative Commons Attribution 4.0 International License.

In some areas, greenhouse lights only turn on after midnight, because the glow from the greenhouses disturbs the nearby residents. I have heard that newly built greenhouses in the Netherlands are required to keep their artificial light in-house. With better design, instead of emitting light into the atmosphere the light can be redirected towards the plants, saving energy and reducing the impact on the nearby nighttime environment.

Update (December 10): After seeing this post, @RICE_MM shared the photo below on twitter, which was produced by Remi Boucher. It shows how a single greenhouse complex near the small town of Anson in Maine produces light roughly comparable to that of the whole city of Sherbrooke, Quebec (population ~150,000). The image also shows the area of the Mont-Mégantic International Dark-Sky Reserve.

Greenhouse and Sherbrooke by Remi Boucher.
Image and Data processing by NOAA's National Geophysical Data Center.

@RICE_MM also shared this post showing the change in the area from 2010 to 2012:

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