# Light Pollution=Energy Wasted

1. Nov 19, 2012

### Bobbywhy

Each and every photon of light we send upward into space at night pollutes the night sky and is wasted. This is excerpted from the Energy Brochure of the International Dark Sky Association (IDA):

“Wasted outdoor lighting, that shines directly upward, is estimated at 22,000 gigawatt-hours a year. At an average of $0.10 per kilowatt-hour the cost of that wasted energy is$2.2 billion a year. In terms of how that affects our carbon footprint, here’s the math:
• 3,412 Btu to generate one kilowatt-hour
• 1 ton of coal = 20.1 million Btu
• 1 barrel of oil = 5.8 million Btu
• 3.6 million tons of coal, or 12.9 million barrels of oil are wasted every year to generate the energy for this lost light.”
http://www.darksky.org/

Night lights map: http://www.cc.gatech.edu/~pesti/night/

For a detailed technical description of the light emitted upward into space see: http://laps.noaa.gov/albers/slides/ast/places.html

For very high resolution images of the night lights download the “hi res” images from:
http://www.lightpollution.it/worldatlas/pages/fig1.htm

The IDA offers simple suggestions on how to diminish the energy wasted in lighting the outdoors at night. The United States could save much energy and money by adopting more sensible lighting schemes. We would thereby reduce our need for foreign energy imports and decrease our carbon emissions footprint. Safety and security lighting would not be affected; only the light sent into outer space would decrease. And the night skies in all their splendor would become more visible.

Cheers,
Bobbywhy

2. Nov 19, 2012

### Staff: Mentor

What are these suggestions?

3. Nov 19, 2012

### Bobbywhy

4. Nov 20, 2012

### Staff: Mentor

The wording in the OP is a little problematic: light reflected off the ground is not necessarily wasted, it is only light directed upwards.

So anyway, it turns out that the light pollution problem is largely going to mitigate itself due to the energy cost implications. On the commercial/industrial end, anyway: people still don't put much effort into it residentially.

5. Nov 20, 2012

### phinds

I'd say you got THAT right. For example, I've never seen parking lot lights that don't direct all of their light downwards by having reflectors above the bulbs. for that matter I don't think I've ever seen common street lights that direct any light upwards.

I don't argue that we might save a bit with residential outdoor lighting but it strikes me that as a percentage of all lighting in the US ... all commercial, residential indoor, and residential outdoor, it would be approximately zero. Does anyone think I have this wrong?