Dark Sky Ordinances

Dark Sky Ordinances - Learning Objectives

1. What is a Dark Sky & Light Pollution?
2. What is a dark sky light fixture?
3. What is a Light dome?
4. What are some light pollution solutions?
5. Where do I find dark sky lighting ordinance examples? Model Lighting Ordinance.

Dark Sky

Preserve our dark sky, at night, put light where it is needed, keep it warm, keep it dim.

In 1977, my home town of Orinda was planning a new park.  When I asked them to use Full Cutoff Luminaires, they requested something in writing to explain what and why I was asking; then I wrote my Outdoor Lighting Guide. The ideas behind this Dark Sky Lighting publication came from my Outdoor Lighting teacher, John Brass, the inventor of the full-cutoff segmented reflector, first used to retrofit the lighting on the Golden Gate Bridge. Thank you John Brass for teaching me how to control outdoor lighting.

When we use carefully aimed, dimmer lights - instead of excessively bright, glaring ones - we can see better, maybe even see the stars.  Balance and restraint is the key to most things in life, and restraint also applies to lighting, especially in our night sky.
Visit my Dark Sky page at TOlighting.com

What is Light Pollution?

The inappropriate or excessive use of artificial light – known as light pollution – can have serious environmental consequences for humans, wildlife, and our climate.
Lighting ordinances often include these components:

• Brightness - excessive light levels
  
• Glare – direct viewing of the light source that causes visual discomfort
• Skyglow – brightening of the night sky over inhabited areas
• Light trespass – light falling where it is not intended or needed
• Clutter – bright, confusing and excessive groupings of light sources
  

Dark Sky Lighting Fixtures

Dark Sky Lighting Fixture Certification - Fixture Seal of Approval -

http://darksky.org/fsa/

What is a Dark Sky Light Fixture? 
The goal is to avoid sending light into the sky; therefore, we call it 'dark sky.' The specifics vary according to jurisdiction.  There are some basics qualities of dark sky lighting that seem universal. All light should be below the fixture, the light should be aimed down.

Why Dark Sky?

International Dark Sky Organization www.darksky.org
Find a chapter near you and learn more.

Illuminating Engineering Society and International Dark Sky Organization Model Lighting Ordinance

IES + IDA - Model Lighting Ordinance 2011

Human Vision and Low Light

"In low light levels, the sensitivity of the retinal cone cells tapers off, and the rod cells take over. There is only one type of rod cell, so the vision it provides is monochromatic; by moonlight, we see only in "black and white". This chart shows the spectral sensitivity range of each of the cone cells which together provide "photopic" (daytime) vision, and the more sensitive rod cells which provide our "scotopic" (nighttime) vision4. In moderate light levels, such as at dusk outdoors or under many artificial light conditions, both the rod and the cone cells contribute to human visual perception. The spectral response of the human visual system under such circumstances is complex and only partly understood. In general, though, this "mesopic" (twilight) vision has a spectral sensitivity peak intermediate between that of photopic and scotopic vision, the shape of this response is affected very strongly by not only the amount of light available, but also by the visual task -- what it is you're seeing and reacting to. As an example, at a given lighting level, the effect of the light source spectral distribution on the ability to read a sign is likely to be much different than the effect on your ability to detect a deer at the side of the road. Much more research is needed to increase our understanding of vision at the intermediate lighting levels relevant to outdoor lighting.

LIGHT COLOR AND VISUAL PERCEPTION:
The human eye, in daylight (photopic) conditions, achieves its peak sensitivity in the yellow-green range, at around 555 nanometers wavelength (with all three cone cell types working together). Peak scotopic sensitivity (nighttime vision) is around 510 nm, in the blue-green; the mesopic peak floats somewhere between the day and night peaks (in the greens), depending on the lighting level, the portion of the eye's field of view involved, and the visual task. It makes sense to consider these peaks when providing artificial light, so we can provide the best visual acuity while using the least energy to produce light. But, there is more to color and visual perception than light sensitivity alone." [1]

Light domes measure light from cities at various distances : Mt. Dellenbaugh, Grand Canyon   http://www.nature.nps.gov/night/science.cfm

Light Pollution Solutions

"One of our core principles is that responsible lighting practices must include consideration of each of the major areas of concern which commonly plague current outdoor lighting: Energy inefficiency and waste; unnecessary light trespass which impacts the natural environment, human health, and/or human experience of the night sky and night itself; and safety and esthetics. We believe that 'solving' one of these problem areas without addressing the others is a mistake." [1]

"To achieve the most effective outdoor illumination, and to minimize harmful side effects from that lighting, we need to have a good understanding of the nature of light, the effects of various types of light, and the light sources we use. Additionally, with the advent of a whole new generation of lighting -- the LED -- it is all the more important that we not only consider light quality, but use good information to guide the development and implementation of this new technology. " [1]

City of Davis LED Retrofit

City’s LED Retrofit Shows Need For Careful Lighting Choices
The initial LED streetlight installation went awry, but this story has a happy ending. Davis California, article by James Benya. [2]

To stop light pollution - turn off your lights. You can see the stars if there are no lights, like in Joshua National Park.

Related Topics

Landscape Lighting,  Dark Sky & Light Pollution, Dark Sky Reserves, Environmental Consequences of Night Lighting, Color Temperature, Sources, Astronomy & Dark Sky, Circadian System, 

Footnotes

1. Low Light Vision  Why does outdoor Lighting Matter? http://www.illinoislighting.org/index.html
   
2. City of Davis LED Retrofit http://darksky.org/citys-led-retrofit-shows-need-for-careful-lighting-choices/

Photo Credits

• Luminaire Shielding Designs Image Courtesy of Bob Crelin
  
•  http://www.illinoislighting.org/lightcolor.html