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                        FHWA Lighting Handbook August 2012


            
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                6 Lighting System Selection
6.1 Design Considerations

Lighting designs need to be performed in full coordination with the features of roadway and surrounds

In some cases, site conditions may dictate if roadway lighting can be installed, or may place certain constraints on the design. Therefore, the following site conditions should be investigated:

Availability of Power – The availability of power is a major factor in determining if roadway lighting can be provided. If power is not available, the local utility should be consulted and cost estimates for power supply should be determined.
	Proximity to Aircraft Landing Facilities – Prospective installations in close proximity to airports and helicopter landing pads may pose problems with defined glide paths and air traffic control operations. Typically, an airport authority or their governing authority will have specific pole height limitations and/or optical requirements for the luminaires. Where a lighting installation is proposed in close proximity to an aircraft landing facility, the facility should be contacted so requirements specific to that facility can be met.
	Proximity to Railroads – Lighting systems near railroad tracks will have specific clearance requirements from the tracks.
	Presence of Overhead Distribution and Transmission Lines – Distribution and transmission lines often conflict with lighting poles. Where transmission or distribution lines exist, or are proposed, and lighting is required, the designer should consult the local utility provider and investigate applicable codes and standards to determine clearance requirements. Typically the higher the voltage of the overhead lines, the greater the clearance distance required. In the case of overhead transmission lines, the local electrical utility may define additional clearance requirements due to the potential sag of the transmission lines. Line sag will vary with the change in ambient temperature and power demand.
	Environmental Issues – The presence of offsite glare, light trespass and skyglow should be taken into consideration in urban areas. The designer should consider these issues prior to undertaking any design and be aware of community concerns and local requirements. Local lighting ordinances may also dictate the type of lighting which may be installed, and may dictate light trespass and skyglow limits.
	Maintenance and Operations Considerations – Maintenance should be considered as part of the roadway lighting design. Where possible, maintenance personnel should be consulted by those undertaking the roadway lighting design. In some cases, products with a higher initial purchase cost can significantly reduce operating or maintenance costs over the life of the project. Products specified should be both corrosion-resistant and durable. All luminaires will require regular service for lamp replacement and cleaning. It is critical that the luminaires be safely accessible via available service vehicles (used by those undertaking the maintenance with minimal disruption to traffic. The height limits of maintenance equipment may impact pole height and location.
	Roadside Safety Considerations – Poles can be a potential hazard to errant motor vehicles. Clear zones and pole placement issues should be known and addressed. Additional information can be found in the AASHTO Roadside Design Guide.
	Historical Safety Performance – It is recommended that historical crash data be reviewed in an effort to identify what may be problematic crash locations. This can be done by first driving, walking or cycling the road and establishing possible problematic locations. Municipal agencies, road authorities and maintenance contractors can be contacted to confirm whether these locations have any recorded crash statistics. Problem areas should be identified and solutions discussed with the owner.Lighting systems should be selected based on the most beneficial life cycle cost of the system

6.2 Lighting Selection

A key task for the roadway lighting designer is the selection and specification of products and equipment. Many manufacturers produce outdoor lighting equipment that is marketed and available throughout North America.

The use of high quality products is critical to prolonging the overall operating life of roadway lighting systems. Quality relates to the features and characteristics of a product that impact on its ability to satisfy stated or implied needs. While quality could be overlooked if low price is the primary criterion for product selection, it should always be a key consideration in product selection. In general, focusing on price alone will not deliver best value installations.

In addition to quality, other key considerations when specifying a product include:

Certification – Electrical products must be certified by an organization accredited by the Standards Council of Canada, and shall bear an appropriate label such as Underwriters' Laboratories (UL).
	Photometric Performance (for luminaires) – A photometric comparison of luminaires is critical to selecting the best product for a given application. Cobra head luminaries can be compared using the CSA 653 model. Comparisons should be based on photometric data provided by the supplier from an independent testing laboratory. The IESNA cutoff classification for luminaires should be known and deemed appropriate for the situation. In general, cutoff or full-cutoff optics should be used wherever possible.
	Durability – Durability is the capability of a product to resist deterioration, damage, and corrosion over time. Designers should understand the potential for vandalism and the corrosive nature of the project's environment, and relate those variables to the specific products under consideration.
	Aesthetics – Products selected should be aesthetically compatible with their surroundings. Manufacturers offer a wide range of equipment with respect to shape, configuration, colors, and styles. Similar or identical-looking products should be used, if possible, when the new installation will be integrated with existing installations. The height of lighting structures should be visually compatible with the height of other structures in the area.
	Availability – Custom and/or decorative products or products manufactured in small quantities often have long lead times for replacement. Designers should verify that the products selected will be available to avoid construction schedule impacts. Also, they should confirm that parts or complete replacement units will be available following installation. If products or parts will not be readily available, the designer should advise the owner to consider purchasing replacement units or parts to stock for maintenance purposes.
	Maintenance Requirements – Maintenance considerations include ease of access for servicing, as well as maintenance frequency and level of service required over the product's anticipated useful life.
	Operations Cost – Similar products can result in varying cost of operations. This is particularly true of products that consume energy. The designer should review operational costs when specifying products and choose those products that are both economical to operate and provide the required performance.The capital cost of an item (also known as the supply cost) is not listed above but is also an important consideration. Supply costs, however, should not be the primary factor when selecting products. To assess a product's true cost, other factors must be considered to confirm best value and performance, or life cycle of a product.

Whenever possible, individuals specifying products are encouraged to designate more than one manufacturer with similar or equal products to reduce costs via competitive bidding. All products proposed, however, should be reviewed for conformance to stated specifications and performance requirements. In some cases a specific product or manufacturer may need to be sole sourced because of the product's enhanced performance, special appearance, or the need to match existing adjacent conditions.

Specific luminaire requirements are as follows:

Ingress Protection (IP) Rating – Optical systems should be well sealed to prevent the entry of dust and water. Luminaires should have an IP rating of 65 or 66 for maximum performance.
	Lens Material - Lenses should be composed of glass. Polycarbonate and acrylic materials, though more impact-resistant, tend to discolor over time, which will reduce light output and will often require replacement in about 5 years.
	Housing – The housing should be made of aluminum with a powder coat exterior finish. The luminaire should be designed for secure attachment to the pole. The luminaire should be designed for easy access for electrical and lamp changes via a tool-less entry
	Internal Electrical – Internal components will include a ballast, a starter and, a capacitor. The ballast should be a constant wattage auto-transformer (CWA) type.
	BUG Ratings – The luminaire optics should meet the specific BUG ratings where they are available.6.3 Luminaire Classification

To assess and mitigate glare and to reduce skyglow, the IESNA have developed cut-off classifications for luminaries based on how they emit light.

The amount of glare generated by a luminaire is strongly influenced by the intensity (candlepower) emitted at angles close to the horizontal.

6.3.1 Luminaire Classification System

A new method referred to as the Luminaire Classification System (LCS) has been developed to define luminaire distribution and efficiency better. IESNA TM-15 Luminaire Classification System for Outdoor Luminaires defines this system in more detail. The LCS replaces the traditional IESNA luminaire cutoff classification system which uses designations like cutoff, non-off, semi-cutoff, and full cut-off. The traditional system was very limited as it only assessed the light distribution at very high angles and above horizontal.

The LCS defines a method of evaluation and comparison of outdoor luminaires. It provides a basic model which defines maximum lumens within defined angles within primary areas. The primary LCS areas are forward light, back light, and up-light zones as defined in Figure 27 (top left). Each of these zones is further broken into solid angles within the area. An example of the forward light zone is shown in Figure 27 (top right).

The sum of percentages of lamp lumens within these three primary areas is equal to the photometric luminaire efficiency. The LCS enables designers to evaluate and compare the distribution of lumens for various types of luminaire optics, thus assisting in the selection of the luminaire most appropriate for the application. An example of measurements for various luminaires is defined in Figure 28.

The benefit of this system, is that it allows a designer to better select the optimal optics for a given application while at the same time reducing light trespass impacts and sky glow. The new classification system is intended to be used as a tool to assess the light output of luminaires.

Figure 27 - Lamp Lumen Zones and Front Light Zone (from IESNA TM-15)**Figure 27 - Lamp Lumen Zones and Front Light Zone (from IESNA TM-15)**

The LCS zones for various luminaire optical systems are calculated and shown in Figure 28. Through lighting photometric analysis software, a designer can use the LCS assess the percentage of lumen output in the various zones. This is very useful when comparing luminaire optical systems and how light is distributed from various luminaries.

Metal Halide
			Internal Refractor Optic (250 W Type V)
			External Refractor Optic (250 W Type V)
			Louvered Reflector Optics (250 W Type III)
			Hydro-formed Refractor Optics with Horizontal Lamp (250 W type I)
			Sag Lens Refractor Optics (250 W Type III)
			Sag Lens Refractor Optics (250 W type I)
			Sag Lens Refractor Optics (100 W type I)Internal Refractor Optic (250 W Type V)
			External Refractor Optic (250 W Type V)
			Louvered Reflector Optics (250 W Type III)
			Hydro-formed Refractor Optics with Horizontal Lamp (250 W type I)
			Sag Lens Refractor Optics (250 W Type III)
			Sag Lens Refractor Optics (250 W type I)
			Sag Lens Refractor Optics (100 W type I)Forward LightLuminaire Lumens
			4133.4
			5405.6
			6306.5
			6487.6
			10115.6
			10557
			3716.3% Lamp Lumens
			19.70%
			25.70%
			30.00%
			29.50%
			46.00%
			48.00%
			45.90%FL (0° - 30°)
			0.20%
			0.90%
			1.20%
			2.40%
			7.40%
			13.10%
			12.60%FM (30° - 60°)
			5.40%
			3.70%
			14.40%
			15.30%
			27.20%
			24.80%
			23.40%FH (60° - 80°)
			8.90%
			17.30%
			12.90%
			11.20%
			11.20%
			10.00%
			9.60%FVH (80° - 90°)
			5.10%
			3.80%
			1.40%
			0.50%
			0.20%
			0.10%
			0.20%Back LightLuminaire Lumens
			4133.40%
			5352.50%
			4220.20%
			4880.50%
			5384.30%
			7138.10%
			2465.60%% Lamp Lumens
			19.70%
			25.50%
			20.10%
			22.20%
			24.50%
			32.40%
			30.40%BL (0° - 30°)
			0.20%
			0.90%
			0.80%
			2.30%
			5.40%
			7.70%
			7.20%BM (30° - 60°)
			5.40%
			3.60%
			9.40%
			13.20%
			14.50%
			17.00%
			16.10%BH (60° - 80°)
			8.90%
			17.10%
			8.80%
			6.00%
			4.40%
			7.60%
			7.00%BVH (80° - 90°)
			5.10%
			3.90%
			1.00%
			0.70%
			0.10%
			0.10%
			0.10%Up-LightLuminaire Lumens
			9997.60%
			2477.00%
			957.50%
			163.20%
			0.00%
			0.00%
			0.00%% Lamp Lumens
			47.60%
			11.80%
			4.61%
			0.70%
			0.00%
			0.00%
			0.00%UL (90° - 100°)
			10.70%
			2.40%
			1.40%
			0.50%
			0.00%
			0.00%
			0.00%UH (100° - 180°)
			37.00%
			9.40%
			3.20%
			0.20%
			0.00%
			0.00%
			0.00%**Figure 28 – LCS Comparison (IES TM-15-07)**

6.3.2 BUG Rating System

Similar to the LCS, the IESNA developed the Backlight-Up-light-Glare (BUG) rating system which establishes back (B), up-light (U), and glare (G) zonal lumen limits for luminaires.

Each category (backlight, up-light, and glare) consists of specific regions that surround the luminaire. Each region has specific upper limit criteria that must be met to obtain the rating. All of the criteria must be met for a luminaire to obtain the generalized B, U, or G rating. So, the rating for a specific metric is set by the lowest (highest zonal lumen value) performance criterion within the metric. The limits vary according to the lighting zone (LZ1 – LZ4) in which the luminaire is located.

Once this calculation is performed for each of the three metrics, the composite BUG rating can be reported. Forward, Back and Up-light Zones and Forward Light Zones show the BUG regions. Solid angle references are based on a sphere of data points around a luminaire.

Figure 29 - Bug Zones (IES TM-15-07)**Figure 29 – Bug Zones (IES TM-15-07)**

Backlight considers the light leaving a luminaire in the opposite direction from the main aiming angle of the light. This is the percent lamp lumens or the luminaire lumens distributed behind a luminaire between 0° vertical (nadir) and 90° vertical. Within a lighting zone, the backlight rating will change depending on the luminaire's proximity to the property line. Backlight is evaluated for high (60°-80°), medium (30°-60°) and low (0°-30°) areas.

Figure 30 - BUG Backlight (IES TM-15-07)
Figure 30 – BUG Backlight (IES TM-15-07)

Up-light measures the total light propagating from the luminaire in a near-horizontal or above-horizontal direction. This is an overall measure of the amount of light directly leaving the luminaire that may be associated with sky-glow. This measures the percent lamp lumens or the luminaire lumens distributed above a luminaire between 90° and 180° vertical. Up-light is evaluated for high (sky-glow: 100°-180°), low (90°-100°), forward light very high (80°-90°), and backlight very high (80°-90°).

Glare considers the light leaving a luminaire in the angles that are most likely to be a source of nuisance (or potentially disabling) to passers-by either within or outside the property boundaries. The light that causes glare is also sometimes presumed to be a source of light trespass problems. However, in most cases, glare complaints are due to the brightness of the source, and not because of spill light levels. For this reason, it is treated separately from the Backlight metric . Glare is evaluated for forward light very high and backlight very high (80°-90°), forward light medium (60°-80°), and backlight medium (60°-80°).

Note that the Up-light and Glare regions overlap as do the Glare and Backlight regions. While Glare is generally only considered important up to horizontal, the Up-light region has been shown to be important below horizontal, down to about 80°. Since these criteria regions are not intended to be additive or comprehensive to the complete output of the luminaire, this overlap is not a calculation inconsistency.

The region from directly below the luminaire forward to 60° is not considered in any of the criteria regions. This region is generally considered the 'safe' region of lumen output, where the light from a luminaire will be falling on the task area in an effective manner, and is also the region where the majority of lumens are outputted. Beyond this unmeasured region, the light may begin to be a source of glare, light trespass, sky-glow, or other concerns.

6.4 Lighting Master Plans

Lighting master plans are formal documents created through a study and planning process. They are based on input from municipal staff, public officials, lighting professionals, citizens, business owners, and others. Lighting master plans define the purpose of lighting, and contain area maps with road types, classifications, land use, pedestrian and cyclist routes, parks, and other infrastructure information. They also contain information regarding fixtures and poles, light sources, fixture cutoff, lighting levels, design criteria, design and construction specifications, historical considerations and recommendations. This information is combined in a single, organized package that becomes the basis for lighting projects.

Lighting master plans take into account anticipated economic and cultural changes, a community's public image and economic development goals, and technological advancements. The benefits of such plans include the coordination of the various municipal lighting functions, proactively planning lighting for the different areas of a community by recognizing their unique character and needs. The plans also provide scheduling of capital expenditures, as well as implementation and maintenance strategies. Lighting master plans are based on the core concept that public facilities should enhance safety, encourage economics, contribute to beautification, and provide a secure environment for people and property. Transportation-related lighting is viewed as a key component of community management.

Lighting master plans are typically adopted by a jurisdiction through a bylaw, resolution, or similar measure, and as such may dictate specific design requirements for roadway lighting. The purpose of a lighting master plan is to ensure adequate lighting is provided for future development, and that public lighting will be installed in a consistent manner that takes into account the needs and desires of citizens. If an area is designated for historic preservation, the lighting master plan may define luminaires and light sources that are compatible with and preserve the area's historical character, or that enhance the existing historical character.

Lighting master plans typically address the following major subject areas:

Improved safety provided by lighting.
	Improved sense of security provided by lighting.
	Costs (capital and operating).
	Aesthetics (daytime and nighttime).
	Lighting design criteria.
	Environmental issues and constraints, including the control of spill light, glare and skyglow.
	Energy use (through definition of unit power density).
	Potential for economic development and the enhancement of nighttime activities through lighting
	Preservation of areas of darkness, such as areas around observatories.
	Maintenance requirements.Designers should check with local officials prior to beginning the design process to determine if a lighting master plan is in place, or is anticipated. Designers should be aware of the requirements of lighting master plans as they relate to the specific project under consideration. At the same time, under no circumstances should lighting master plan requirements dictate the quantity or quality of light for a roadway facility, since the safety of the roadway user is of paramount importance.
      
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                Book:FHWA Lighting Handbook August 2012
              Policy and Guidance
                2 Federal Guidance and Recommendations Regarding Roadway Lighting
                Basic Terms and Concepts Related to Roadway Lighting
                3 Vision and Fundamental Concepts
                Warranting Criteria
                4 Analysis for Lighting Needs
                5 Considerations Concerning Lighting Systems
                6 Lighting System Selection
                Lighting Application Considerations
                7 Lighting Application
                Other Systems and Issues Related to Roadway Lighting
                8 Related Roadway Systems
                9 Summary
                References
                Glossary of Terms U.S. DEPARTMENT OF TRANSPORTATION

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