Protecting the Night Sky Resource of Cherry Springs Dark Sky Park

Stan Stubbe and Gary Honis, P.E.

Pennsylvania Outdoor Lighting Council

1. Purpose of Document:

This document was prepared by the Pennsylvania Outdoor Lighting Council (POLC) as a guide and reference for the Pennsylvania Department of Conservation and Natural Resources (DCNR) for use in the protection of the night sky resource of the Cherry Springs Dark Sky Park (CSDSP). In particular, the document addresses environmental considerations in regard to the mitigation of light pollution from the proposed Potter County windfarm.

Details of the proposed windfarm such as location and elevation of wind turbines, type and amount of lighting proposed, and other specifics of the windfarm's design and planned construction activities and support facilities were not made available to the POLC. Lacking technical details of the proposed project, this document was prepared to address all potential impacts to the nighttime environment of CSDSP.

2. Threatened Night Sky Resource of Park

Cherry Springs State Park was designated by DCNR as the first Dark Sky Preserve in the Commonwealth. In 2001, PA House Bill 300, "Outdoor Lighting Control Act", was unanimously passed in the House by a vote of 195-0. The following language was contained in the Bill: "The Department of Conservation and Natural Resources shall identify and designate Cherry Springs State Park in Potter County as a Dark Sky Preserve. The Department of Conservation and Natural Resources shall manage Cherry Springs State Park in a manner to eliminate or prevent light pollution and preserve the exceptional conditions necessary for astronomical observations."

The actions taken by the Commonwealth to protect the night sky resource have been predicated on the realization that this small area of the Commonwealth is the last area remaining in the Commonwealth with a natural night sky. In addition, it is one of only a few areas remaining in the Eastern United States free of light pollution.

The light pollution map of Pennsylvania below is based on nighttime images obtained from the Defense Meteorological Satellite Program and is taken from the map of North America by the Light Pollution Science and Technology Institute:

The small single black spot located in Potter County in the above image represents the skies of Cherry Springs Dark Sky Park and the only area remaining in the Commonwealth of Pennsylvania with a natural night sky free of light pollution and classified at a Level of 2 on the Bortle Scale as described below:

Color	Artificial / Natural Sky Brightness	Sky Brightness mags / sq arcsec V Band	Bortle Scale approx	Description (Descriptions are approximate. Your sky may vary.)
	< 0.01	22.00 to 21.99	1	Gegenschein visible. Zodiacal light annoyingly bright. Rising milkyway confuses some into thinking it's dawn. Limiting magnitude 7.6 to 8.0 for people with exceptional vision. Users of large dobsonian telescopes are very happy.
	0.01 to 0.11	21.99 to 21.89	2	Faint shadows cast by milkyway visible on white objects. Clouds are black holes in the sky. No light domes. The milky way has faint extensions making it 50 degrees thick. Limiting magnitude 7.1 to 7.5.
	0.11 to 0.33	21.89 to 21.69	3	Low light domes (10 to 15 degrees) on horizon. M33 easy with averted vision. M15 is naked eye. Milky way shows bulge into Ophiuchus. Limiting magnitude 6.6 to 7.0.
	0.33 to 1.0	21.69 to 21.25	4	Zodiacal light seen on best nights. Milkyway shows much dark lane structure with beginnings of faint bulge into Ophiuchus. M33 difficult even when above 50 degrees. Limiting magnitude about 6.2 to 6.5.
	1.0 to 3.0	21.25 to 20.49	4.5	Some dark lanes in milkyway but no bulge into Ophiuchus. Washed out milkyway visible near horizon. Zodiacal light very rare. Light domes up to 45 degrees. Limiting magnitude about 5.9 to 6.2.
	3.0 to 9.0	20.49 to 19.50	5	Milkyway washed out at zenith and invisible at horizon. Many light domes. Clouds are brighter than sky. M31 easily visible. Limiting magnitude about 5.6 to 5.9.
	9.0 to 27.0	19.50 to 18.38	6 or 7	Milkyway at best very faint at zenith. M31 difficult and indistinct. Sky is gray up to 35 degrees. Limiting magnitude 5.0 to 5.5.
	>27.0	<18.38	8 or 9	Entire sky is grayish or brighter. Familiar constellations are missing stars. Fainter constellations are absent. Less than 20 stars visible over 30 degrees elevation in brighter areas. Limiting magnitude from 3 to 4. Most people don't look up. CCD imaging is still possible. But telescopic visual observation is usually limited to the moon, planets, double stars and variable stars.

The night sky over CSDSP is one of only a few areas remaining in the Eastern United States that is free of light pollution as shown in the image below. The night skies of CSDSP are depicted in the image as a small black spot.

The above image is testament to why CSDSP is known both nationally and internationally for its pristine night sky resource and why it has been the subject of many news and magazine articles published worldwide. One such 2006 Associated Press article by Dan Nephin, AP writer, has had a circulation of 2.4 Million and impressions of nearly 50 Million over a two-month period:

Date	Media Outlet	Circulation	Impressions
	Associated Press Cherry Springs article
8/12/2006	PhillyBurbs.com (Philadelphia, PA)	N/A	377,786
8/13/2006	Eagle (Reading, PA)	90,856	218,054
8/13/2006	Sunday Times (Scranton, PA)	74,275	178,260
8/13/2006	Altoona Mirror (Altoona, PA)	39,109	93,861
8/13/2006	Mercury (Pottstown, PA)	24,539	58,893
8/13/2006	Sunday Pocono Record (Stroudsburg, PA)	25,830	61,992
8/13/2006	Reporter Sunday (Lansdale, PA)	18,659	44,781
8/13/2006	CentreDaily.com (State College, PA)	N/A	33,782
8/14/2006	Sentinel (Carlisle, PA)	15,072	36,172
8/14/2006	Beford Gazette (Bedford, PA)	10,500	25,200
8/14/2006	Beaver County Times (Beaver, PA)	41,950	100,680
8/20/2006	Tri-County Sunday (DuBois, PA)	12,200	29,280
8/20/2006	Times Herald (Norristown, PA)	16,391	39,338
8/20/2006	Post-Gazette Online (Pittsburgh, PA)	N/A	1,499,184
8/31/2006	The Record Online (Parsippany, NJ)	N/A	42,590
9/11/2006	Yahoo! News	N/A	8,383,046
9/11/2006	Canadian Press	N/A	2,056
9/11/2006	KTVZ-TV Online (Portland, OR)	N/A	N/A
9/12/2006	DenverPost.com (Denver, CO)	N/A	891,720
9/13/2006	ABC News Online	N/A	4,362,505
9/13/2006	Philly.com (Philadelphia, PA)	N/A	1,254,721
9/15/2006	Cecil Whig (Elkton, MD)	17,500	42,000
9/15/2006	Telegram.com (Worchester, MA)	N/A	77,657
9/15/2006	DallasNews.com (Dallas, TX)	N/A	1,169,123
9/15/2006	Post-Gazette.com (Pittsburgh, PA)	N/A	1,499,184
9/16/2006	Free Lance Star (Fredericksburg, VA)	47,925	115,020
9/16/2006	Daily Record (Baltimore, MD)	18,000	43,200
9/16/2006	Canada.com	N/A	1,083,835
9/17/2006	Sunday Voice (Wilkes-Barre, PA)	29,608	71,059
9/17/2006	Sunday Review (Towanda, PA)	10,200	24,480
9/17/2006	Valley News Dispatch (Tarentum, PA)	34,000	81,600
9/17/2006	Centre Daily Times (State College, PA)	33,782	81,760
9/17/2006	Sunday Recorder (Amsterdam, NY)	9,506	22,814
9/17/2006	Sunday Tribune-Review (Greensburg, PA)	107,139	257,133
9/17/2006	Sierra Vista Herald (Sierra Vista, AZ)	12,516	30,038
9/17/2006	Bisbee Daily Review (Bisbee, AZ)	1,205	2,892
9/17/2006	Sun (Yuma, AZ)	25,061	60,146
9/17/2006	High Point Enterprise (High Point, NC)	30,573	73,375
9/17/2006	Paragould Daily Press (Paragould, AR)	6,500	15,600
9/17/2006	Times Daily (Florence, AL)	34,126	81,902
9/17/2006	Beaufort Gazette (Beaufort, SC)	12,036	28,886
9/17/2006	Index-Journal (Greenwood, SC)	14,384	34,521
9/17/2006	Rapid City Journal (Rapid City, SD)	33,599	80,637
9/17/2006	Columbus Dispatch (Columbus, OH)	361,304	867,129
9/17/2006	Sunday Observer (Dunkirk, NY)	15,000	36,000
9/17/2006	Northwest Herald (Crystal Lake, IL)	37,964	91,113
9/17/2006	Herald-Tribune Online (Cincinnati, OH)	N/A	4,000
9/17/2006	Lansing State Journal Online (Lansing, MI)	N/A	N/A
9/18/2006	Herald-Standard Online (Uniontown, PA)	28,765	69,036
9/18/2006	Delaware Online	N/A	287,347
9/18/2006	CNN.com	N/A	20,624,395
9/19/2006	Wilmington Star Online (Wilmington, DE)	N/A	N/A
9/23/2006	Review Times (Fostoria, OH)	42,060	100,944
9/24/2006	Intelligencer (Doylestown, PA)	45,000	108,000
9/24/2006	Burlington County Times (Willingboro, NJ)	44,711	107,306
9/24/2006	Eagle (Reading, PA)	90,856	218,054
9/24/2006	Bucks County Courier Times (Levittown, PA)	73,249	175,797
9/24/2006	Erie Times-News (Erie, PA)	88,622	212,692
9/24/2006	Idaho Press-Tribune (Nampa, ID)	17,816	42,758
9/25/2006	Evening Sun (Hanover, PA)	19,767	47,440
9/25/2006	Eagle Online (Reading, PA)	N/A	64,600
9/25/2006	Courier Post Online (	N/A	80,635
9/29/2006	Staten Island Advance (Staten Island, NY)	67,033	160,879
10/1/2006	Sun (Baltimore, MD)	467,911	1,122,986
10/1/2006	New Haven Register (New Haven, CT)	99,532	238,876
10/1/2006	Scottsdale Tribune (Scottsdale, AZ)	18,429	44,229
10/1/2006	The Providence Journal Online (Providence, RI)	N/A	279,509
10/1/2006	Baltimore Sun Online (Baltimore, MD)	N/A	888,282
10/6/2006	Daily News (McKeesport, PA)	25,000	60,000
10/8/2006	Cleveland Plain Dealer Online (Cleveland, OH)	N/A	463,482
10/8/2006	Asbury Park Press (Asbury Park, NJ)	N/A	310,390
	Total	2,390,060	49,416,642

The unique factors of CSDSP for astronomical use are as follows:

1. Elevation of 2400 feet with 360 degree horizonal views.

2. Located in the only remaining area of the Commonwealth free of light pollution with a night sky rated at a Bortle value of two, on a scale of one to nine.

3. The park is used by members of the astronomical community nationwide with occasional use by international visitors.

3. Visual Astronomy

CSDSP is used throughout the year by amateur astronomers and the general public at night to view celestial objects with the naked eye, telescopes and binoculars. The park is known for its panoramic views of the sky at night and the expanse of the Milky Way stretching across the sky from horizon to horizon. Such views are not available anywhere else in the Commonwealth. Under favorable weather conditions, the night sky of the park is known to provide naked eye views of the stars to the horizon in all directions on the observing field. Use of telescopes and binoculars are used as well to magnify the view of celestial objects near the horizon. Some astronomical events such as the Aurora Borealis (Northern Lights), make appearances close to the horizon. The Aurora Borealis is a celestial event that is most affected by even low levels of light pollution and because of the absence of artificial light, produces spectacular views in the Northern sky from CSDSP.

Light pollution is the most serious hazard to visual observation of faint sources of light from celestial objects. The absence of man-made light visible from CSDSP facilitates excellent dark adaptation. Although the human eye can expand its pupil size within a few seconds of dark, in order for the eye to become dark adapted, chemical changes in the retina involving the eye's rods and cones, need to take place in an area free of ambient light sources. The eye can detect light when certain precursor chemicals are transformed by light to other chemicals. These chemicals in turn cause signals to be sent to the brain representing the image seen by the eyes. The sensitivity of our eyes is directly related to the concentration of precursor chemicals. Even low level ambient light conditions can retard chemical adaptation, and a sudden burst of direct light can break down practically all of the precursor chemicals and ruin the dark adaptation, requiring another period of time for the eyes to dark adapt. For complete dark adaptation there must be no man-made ambient light within the field of view. The human eye may need 30 minutes or longer to dark-adapt, depending on the age of the observer. During the first minute of observing in dark sky conditions, the eye's sensitivity increases ten fold. In 20 minutes it increases 6000 fold and after forty minutes of dark adaptation, the eye's sensitivity increases 25,000 times.

4. Public Programs and Astronomy Education

Astronomy programs are offered to the general public on a regular basis at CSDSP that include nighttime observations and include the following:

1. Telescopic views of the Moon, planets, galaxies, star clusters and nebulae.

2. Tours of the star constellations.

3. Observation of special astronomy events such as meteor showers and comet appearances.

4. Observation in the northern sky of the Aurora Borealis (Northern Lights).

5. Observation of satellite passes.

6. Monthly Stars-N-Parks programs for the public sponsored by the National Public Observatory in New Mexico.

7. Major astronomy events held in June by the Astronomical Society of Harrisburg and in September by Central Pennsylvania Observers.

The park is used throughout the year by amateur astronomers who use telescope and camera equipment to observe and photograph the planets and deep sky celestial objects such as galaxies and nebulae. Long exposure film photographs and images taken by astronomical CCD imaging devices are taken at the park. Such film and CCD exposures can exceed a few hours in length and are extremely susceptible to the effects of light pollution.

5. Astrophotography and CCD Imaging

Light pollution can affect astrophotography and CCD imaging in a number of ways including:

1. Light Pollution causes sky glow, which creates sky fogging of the image that reduces the possible length of the exposure time that can be used to capture the image. Since the resulting maximum exposure time is shortened, this results in a poorer quality image with less detail captured. Sky glow can be severe to the level of causing fainter deep sky objects to be undetectable visually and undesirable to image with film or CCD imaging equipment.

2. Light pollution from a source in one direction can cause a sky fog gradient that appears across the frame of the photograph or image. Such gradients can result in poor or unusable images.

3. CCD imaging devices are highly sensitive to light and combined with lenses and telescopes can capture images of the faintest celestial deep sky objects. Amateur astronomers at CSDSP can now capture images and conduct astronomical studies using CCD imaging devices, once only possible by professional observatories. Additional lighting of any type or level from any light source within 20 miles of the park will be captured in the images taken by these devices.

6. Scientific Studies

CSDSP is used by amateur astronomers that work closely with professional astronomers to conduct scientific studies that require skies free of light pollution. These studies are conducted both visually and by astrophotography and CCD imaging and include timing of asteroid occultations, discovery and monitoring of super-novas within faint galaxies, sky searches for comet and near-Earth asteroids and monitoring and study of planned gas releases by satellites. Pristine night skies are essential for such studies.

7. Park Infrastructure and Support

The park has been supported financially by "user fees" charged to park visitors, donations made to the "Dark Sky Fund", and the Commonwealth's general fund. The "Dark Sky Fund" is a non-profit, friends-of-the-park fundraising organization. In 2005, the Commonwealth invested $400,000 for improvements to CSDSP. Infrastructure has been installed including four astronomical observatories, an outdoor amphitheater for astronomy presentations, electric pedestals on the observing field and other facilities to accommodate public viewing events. The park has recently acquired the nearby airfield which may be used for additional infrastructure including observing space to alleviate crowded field conditions on the existing observing field. Consideration of potential impacts to the park should include effects on both the existing observing field and the acquired former airfield area.

8. Offending Sources of Light Pollution

Construction and operation of the proposed windfarm will most likely involve a number of lighting installations contributing to light pollution that will negatively impact CSDSP. These include but are not limited to the following:

1. Any tower lighting required by the FAA.

2. Exterior lighting used for windfarm buildings.

3. Parking area lighting.

4. Roadway and access road lighting.

5. Sign lighting.

6. Power Utility storage yard and exterior building lighting.

7. Exterior lighting associated with construction phase activities including:

a. Earth moving equipment and vehicles

b. Temporary construction office trailers, container buildings and other structures.

c. Area flood lighting for nighttime construction.

d. Lighting needed for nighttime operation of cranes and other assembly equipment.

e. Lighting for any quarry or cement facility operations.

f. Site security lighting.

9. Environmental Impact Studies

It is recommended that environmental impact studies be prepared that address utilization of the park as follows:

Daytime Visual Impact:

Visitors to CSDSP are treated during the day of breathtaking scenery from this clearing on top of one of Potter County's highest ridges. Overlook areas, including those on Route 44 near the park, are favorite stopping places for visitors to enjoy the outstanding beauty of mountain ridgelines where wooded hillsides meet the sky, unspoiled by human interventions. Proposed windfarms are controversial in many communities, mostly due to the concerns the visual impact of turbines will have on the aesthetic qualities of the natural landscape. This will be a concern for daytime use of CSDSP. Its scenery is a visual resource that merits careful consideration and protection, since this area is arguably the most scenic and least developed county in the state.

Nighttime Visual Impact:

Structures:

Impact studies should include a determination of the visibility of the windfarm and support structures in direct view from all areas of the park. Documentation in the form of maps, drawings or other graphic projections should be provided that depict the proposed height of tall structures and wind turbine components including all elevation plots between the park and the windfarm structures. Such representations should clearly define the portion of structures that would be visible from the park. A listing should be provided of the angle in degrees between the horizon and uppermost part of all tall structures. In addition, an accompanying listing should be provided of the azimuth in degrees of all tall structures using the center of the park's observing field as a reference.

Lighting:

The proposed lighting of the tall structures as discussed in the previous paragraph should be described. This description should include the following:

1. Lamp type proposed , i.e., Low Pressure Sodium, High Pressure Sodium, Metal Halide, Incandescent, Red LED, Xenon, etc.

2. Lamp wattage

3. Type of light fixture proposed as defined by the Illuminating Engineering Society of North America (IESNA), such as "full cut-off", “cutoff”, "semi-cutoff", floodlight, spotlight, etc.

4. If intermittent lights are to be used, the flash rate and flash duration should be provided along with an explanation of any synchronization used.

5. Light output intensity of proposed luminaires as measured in candelas.

6. Location of luminaires on tall structures.

A discussion should be provided of the decision process and steps taken to mitigate potential increases in light pollution levels from all exterior light sources proposed. The proposed lighting for the following uses, and any other related uses requiring exterior lighting, both during and after construction of the windfarm should be described:

1. Building exterior lighting and interior lighting that projects light outside

2. Parking area lighting

3. Roadway lighting

4. Power Utility lighting

5. Security lighting

Proposed lighting should be fully described for proposed buildings, parking areas, access roads, power utility facilities and structures, storage yards and earth moving operations. For each lighting application the following information should be provided:

A plan (or plans) of the site, complete with all structures, parking spaces, building entrances, traffic areas (both vehicular and pedestrian), and adjacent uses that might be adversely impacted by the lighting. The lighting plan should contain a layout of all proposed fixtures by location, orientation, aiming direction, mounting height and type. The plan should include, in addition to proposed area lighting, all other exterior lighting, e.g., architectural, building-entrance, landscape, flag, sign, etc.

A 10’x10’ illuminance grid (point-by-point) plot of maintained horizontal footcandles overlaid on the site plan, plotted out to 0.0 footcandles, which demonstrates mitigation of light trespass.

The maintenance (light-loss) factors, IES candela file nomenclature, lamp-lumen ratings and specific lamp manufacturer’s lamp ordering nomenclature, used in calculating the presented illuminance levels.

Description of the proposed lighting equipment, including fixture catalog cuts, photometrics, glare reduction devices, lamps, on/off control devices, mounting heights, pole foundation details and mounting methods.

Submission of a visual-impact plan that demonstrates appropriate steps have been taken to mitigate the potential consequences of on-site and off-site glare.

10. Lighting Implementation Best Practices and Design Recommendations

The POLC offers the following recommendations concerning exterior lighting related to the proposed windfarm. These recommendations are based on minimizing the adverse effect of light pollution to CSDSP from construction and operation of the windfarm. The additional benefit of following these recommended practices is the savings realized in energy used for lighting and the example set for energy conservation.

FAA Tower Lighting Requirements:

Official government guidance documents pertaining to the lighting of wind turbines and considered in preparation of this recommendation are as follows:

• US DOT FAA Advisory Circular 70/7460-1J dated 11/29/95—Obstruction Lighting.
• US DOT FAA Advisory Circular 150/5345-43F dated 09/12/06 - Specification For Obstruction Lighting
• US DOT FAA Advisory Circular 150/5345-43E dated 10/19/95—Specification for Obstruction Lighting Equipment.
• US DOT FAA Code of Federal Regulations, Part 77, dated March 1993—Objects Affecting Navigable Airspace.
• Report Number DOT/FAA/AR-TN05/50 dated November 2005 - Development of Obstruction Lighting Standards for Wind Turbine Farms

The focus of windfarm lighting plans studied by the FAA is on aviation safety and recommendations made by the FAA relate to visibility of windfarm turbines at night and do not address aesthetic concerns or light pollution caused by obstruction lighting. The FAA's recommendations for maximizing the visibility of obstruction lighting for aircraft can understandably be at odds with minimizing the effect of obstruction lighting as a public nuisance problem of light trespass and an aesthetic annoyance, and also its effect on light pollution and resulting skyglow.

Any tower construction or alteration of more than 200 feet above ground level requires FAA approval and lighting may be required. Although white strobe lights are allowed on structures by the FAA, their use at night would be extremely detrimental to the night skies of CSDSP and would end its use as a night sky resource for the astronomical community. The FAA allows use of red lighting for obstruction lighting by two methods: red flashing incandescent lighting and rapid discharge red strobe lighting. A minimum intensity of 2000 candelas is required at night for red flashing or red strobe lighting. The FAA also has a standard (L-810) for red steady-burning obstruction lights, with an intensity of approximately 32 candelas.

Only recently has the FAA begun to address the special concerns of wind turbine lighting which involves multiple tall structures that can be dispersed over a very wide area. Wind turbine installations can cover many square miles that vary in terrain features such as hills, flat plains and mountain ridgelines creating the need for obstruction lighting design specific to the particular windfarm location. In addition, the placement of the lights is contingent upon which type of physical configuration of wind turbines is being used, i.e., linear, cluster or grid arrangements.

Existing windfarm obstruction lighting installations have used a variety of obstruction lighting schemes making use of white strobe lighting, red flashing and red strobe lighting and red steady-burning lights at night. FAA Report Number DOT/FAA/AR-TN05/50 dated November 2005, Development of Obstruction Lighting Standards for Wind Turbine Farms, that studied the obstruction lighting of existing windfarms, offered the following observation in its study's concluding remarks: "The red light fixtures that are programmed to flash simultaneously with each other have been determined to be the most effective and efficient technique for lighting wind turbine farms as obstructions." By "most effective", the FAA's report is referring to the best lighting method for maximizing the visibility of the structures for aircraft. Simultaneous flashing of obstruction lighting in a synchronized manner also unfortunately maximizes the visual effect for ground observers and hence light trespass and light pollution.

The FAA does not require the lighting of all wind turbines of a windfarm but instead will approve plans for lighting specified wind turbine units such as those on the periphery of the installation and the highest wind turbines with unlighted separations or gaps of no more than 1/4 to 1/2 mile.

Aviation Obstruction Lighting Recommendations:

Position wind turbines at locations where obstruction lighting will not be visible from CSDSP.

Size wind turbine towers so that obstruction lighting will not be visible from CSDSP.

Minimize the number of wind turbines to be lighted within lighting design requirements of the FAA.

White strobe lighting should not be used. As per the FAA recommendation DOT/FAA/AR-TN05/50 : "They (white strobes) distract the pilot from his interpretation of the other red flashing and steady-burning obstruction lights and can cause confusion. Even support towers for meteorological devices located within the confines of the turbine farm should not be equipped with nighttime white strobe lights, but rather display flashing red lights."

According to an FAA report DOT/FAA/AR-TN05/50, windfarms have experimented with external upward directed flood lighting of turbine structures with halogen floodlights. The FAA concludes "floodlighting a number of wind turbines within an extensive turbine farm installation might be aesthetically unacceptable." Any upward floodlighting of the proposed Potter County wind turbines would be the demise of CSDSP and its use as a night sky resource.

Existing wind turbine lighting designs have included a mix of both red flashing/red strobe lights each with a minimum intensity of 2000 candelas and of steady-burning red obstruction lights, each with an intensity of approximately 32 candelas. Since the steady-burning red obstruction lights cause less light pollution, their use over red flashing or red strobe lights is preferred and should be maximized in the lighting design.

The FAA has established standards for classifying categories of obstruction lighting and for red flashing or strobe lighting at night, allows a range of periods for the light's on/off state. This lighting period is defined by "flash rate" measured in flashes per minute (FPM) and "flash duration" measured in milliseconds (ms). For red incandescent and red strobe lighting, flash rates of 20 to 40 FPM are allowed under Category L-864 and 60 FPM under Category L-855. To minimize light pollution, the slowest flash rate of 20 FPM allowed by FAA should be used. For red incandescent lighting, flash durations of 1/2 to 2/3 of the flash period is allowed and for red strobe lighting flash durations of between 100 and 2000 ms periods are allowed. To minimize light pollution the minimum flash durations allowed by the FAA should be used.

The FAA has studied flashing obstruction lighting of windfarms at night that operate in unsynchronized and synchronized modes. The FAA concluded that "synchronization of the obstruction lighting array increased the effectiveness of the lighting installation immeasurably and provided significantly improved information concerning the shape and extent of the wind turbine farm as an entity." It is recommended that proposed obstruction lighting for the Potter County windfarm not be synchronized in a manner that all wind turbine lights flash at the same time in unison, but instead flash separately in a sequenced pattern in order to minimize light pollution.

Consider designation by the FAA of the proposed Potter County windfarm as a "no fly" zone so that no obstruction lighting is required.

Unnecessary Lighting:

All lighting plans for the proposed Potter County windfarm for the lighting tasks listed in Paragraph 8 above, "Offending Sources of Light Pollution" should have as their primary objective: minimizing glare, light trespass and light pollution by specifying only the amount of illumination required for safety and security and no greater. Lighting should not be used to serve as the primary means of providing security but rather as an element of an overall security system. Providing site lighting when no one is present to see an intruder is of little or no value. The use of surveillance cameras that operate under minimal light levels for their effective operation is recommended.

Lighting Controls:

All lighting plans for the proposed Potter County windfarm for the lighting tasks listed in Paragraph 8 above, "Offending Sources of Light Pollution" should incorporate the use of lighting controls. Automatic programmable timers with seasonal adjustment and spring or battery backup should be utilized to turn on exterior lighting only when needed. The use of motion sensor devices should be incorporated in the lighting design as appropriate so that illumination is only used when it is required.

Fully Shielded Fixtures:

For the lighting of predominantly horizontal surfaces, light fixtures should be aimed straight down and should be fully shielded fixtures that meet IESNA full-cutoff criteria. Externally illuminated signs should have fixtures mounted at the top of the sign and aimed downward. The fixtures should be designed, fitted and aimed to shield the source from off-site view and to place the light output onto and not beyond the sign. At no point on the face of the sign should the illumination exceed 10-vertical footcandles during hours of darkness. The light source for internally illuminated signs should not exceed 500 initial lumens per square foot of sign face. Only light fixtures approved by the International Dark-Sky Association (IDA) as Dark-Sky friendly fixtures and listed on the IDA web site should be used during the construction and operation of the proposed wind farm.

Lamp Types - Low Pressure Sodium:

Low pressure sodium (LPS) lamps should be used for all lighting tasks listed in Paragraph 8 above, "Offending Sources of Light Pollution", except for wind turbine lighting. LPS provides a "monochromatic" light output that can be filtered for astronomical observations and imaging. LPS is the most energy efficient lighting source, providing more light per watt than any other source. If an LPS lamp fixture is not available for a required lighting task, High Pressure Sodium (HPS) should be used as an alternative.

11. Summary:

The night sky of CSDSP is a fragile and threatened resource of the Commonwealth that needs to be protected by the Commonwealth. The proposed Potter County windfarm will increase light pollution levels that will directly affect use of the park and may cause the loss of the only true night sky remaining in the Commonwealth. We are recommending studies that should be conducted to measure the effect of increased light pollution on the park and are making recommendations on the lighting used for wind turbines and associated windfarm lighting to mitigate the effects of light pollution on the park.

A copy of this report in Microsoft Word DOC format can be obtained HERE.