|Good and Bad
Lighting in the Central Valley
skykeepers.org founded September 1, 1999
The major reason Light Pollution is so bad in the Central Valley is the type of light fixture used by municipalities followed by commercial, industrial, residential and to some extent sports lighting.
The energy wasted by bad fixtures, to some extent contribute to Global Warming.
Bad Light Fixtures used by some Municipalities -
GOOD and BAD side by side example
Drop Lens Cobra "BAD" (left) and Flat Lens Cobra "GOOD" (right)
This photo shows one of the main reasons we have Light Pollution, the use of drop lens cobra fixtures by our municipalities. It does not take expensive equipment or training to understand why drop lens cobras cause light pollution, this photo shows what happens. The photo was take in Old Town Sacramento under the I-5 over crossing. Other examples can be found under the freeway in this area.
Drop Lens Cobra (left) -
Note the shadow directly above the fixture and how bright spots extent out on each side.
If the freeway over crossing was not there this light would travel hundreds of miles beyond the fixture.
This shadow is not created by reflection from the road below but by the glass lens which extends below.
This type of fixture creates glare as drivers approach this on ramp.
This fixture wastes energy by allowing light to go in all directions.
This fixture is a major cause of light pollution.
Flat Lens Cobra (right) -
There is no shadow is visible above the fixture on the right.
It is easy to see the "cutoff" pattern of the projected light on the columns to the left and right of the fixture.
The top of the columns and the bottom of the freeway bridge remain dark compared to lower down.
Light is directed down on to the pavement below and on object that need to be illuminated.
When viewed from a distance the source of the light is not visible (glare is reduced).
This fixture conserves energy by confining all the light to objects that need to be illuminated.
This fixture protects the night sky from light pollution and prevents light trespass.
Fixtures commonly used for street lighting that cause light pollution
Why do we have such bad light pollution in the central valley?
See this link pages 6,7 and 9,10 for part of the answer, City of Sacramento
Here is another link relating to the City of Sacramento, Google "light pollution" site:www.cityofsacramento.org http://www.google.com/search?hl=en&q=%22light+pollution%22+site%3Awww.cityofsacramento.org&btnG=Search
Even more telling, Google "light pollution" site:www.saccounty.net "light pollution" site:www.saccounty.net
Bad Light Fixtures used in some Industrial and Commercial applications
05 OCT 2007Home