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15 The importance of proper lighting arrangements in nighttime work zones is obvious. Con- struction work-zone lighting and glare specifications should require appropriate levels of light- ing based on work tasks. In addition, the agency must have practical methods for inspecting nighttime work-zone lighting arrangements. Key Take-Aways ⢠The more quantitative the contract specifications are about required work-zone lighting levels, the better, because the specifications then provide measurable outcomes that STAs can easily check. ⢠Drive-through inspections are important but are not sufficient for ensuring proper work-zone lighting levels. Nighttime construction lighting arrangements have an impact on project safety, quality, cost, and productivity (El-Rayes and Hyari 2005a). One of the main reasons illumination levels have a strong impact on the other aspects of nighttime construction is the fact that light influences human performance and alertness. Lighting Inspection Tools and Methods The quality of work-zone lighting can be evaluated using three main parameters: illuminance, lighting uniformity, and glare. A good specification requires a minimum level of average illumi- nance on the jobsite. This illuminance specification ensures the intensity of light incident on the surfaces of the project. Light uniformity ensures that lighting is distributed equally across the construction jobsite. Finally, the third quality parameter specified is maximum glare, which is quantified using the levels of luminance prevalent on the site (El-Rayes and Hyari 2005a). Illuminance Illuminance represents the time rate of light flow, measured in lumens, that falls upon a sur- face area. The unit of measurement of illuminance is lux, which is measured in lumens per square meter. Illuminance can be measured on a jobsite using a simple device called an illumi- nance meter (see Figure 3.1). To calculate horizontal illuminance on a jobsite, measurements need to be taken from dif- ferent locations. To ensure the uniformity of the measurement, readings over a uniform grid of points that covers the entire jobsite are recommended. The value of illuminance at any point on the jobsite grid depends on the values of lighting intensity reaching that point from each luminaire being used. The size of the grid for measuring C H A P T E R 3 Illumination
16 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity illuminance depends on the task detail level, but grid point spacing should generally range from 1 to 3 ft. Key Take-Aways Illuminance is the amount of light that falls on a surface. It is measured in lux (metric) or foot-candles (imperial). Most agency specifications require certain levels of illuminance for the performance of construction tasks. The measurement is performed by holding the illuminance meter horizontally at the specified height and taking the measurement. Luminance The amount of lighting available for performing a specific task can be measured using lumi- nance. This measure is often confused with the above-described illuminance measure; there- fore, it is important to distinguish between these two measures. Illuminance is a measure of the amount of light incident on a unit surface area. Luminance, on the other hand, is the amount of light, measured in luminous flux, leaving a surface at a given time. Luminance, therefore, is measured in candelas per square meter and is more suitable for measuring visibility of objects (Ellis 2001). Given that luminance needs a target for which measurements are taken, its measuring devices allow users to focus from a distance on specific targets. Figure 3.2 shows a typical luminance meter. Key Take-Aways Luminance is the amount of light reflected from a surface. Luminance is measured in candela per square meter (metric) or foot-candelas (imperial). Most agency specifications do not have a requirement for luminance, but it is an important parameter to measure because it determines the amount of glare. Uniformity Lighting uniformity is an important lighting quality parameter used to evaluate the suitability of lighting arrangements in nighttime work zones. This parameter is based on the calculation of the levels of illuminance on the jobsite. Lighting uniformity is calculated as the ratio between the above-described average illuminance, Eavg, and the minimum illuminance at the darkest spot on Figure 3.1. Illuminance meter (El-Rayes et al. 2007).
Illumination 17 the jobsite, Emin. The following equation shows the above-described calculation of the uniformity ratio (El-Rayes and Hyari 2005a). uniformity ratio U E E avg( ) = min Note that smaller values of this ratio are better because they indicate a smaller difference between average illuminance and the levels of lighting at the darkest spot on the jobsite (Nassar 2008). Glare Unlike lighting uniformity, glare calculations are dependent on luminance values prevalent on the jobsite. Luminance calculations require consideration of the reflectance characteristics of the surfaces present at the jobsite. The largest surfaces to consider are naturally the pavement surfaces in the work area, which are classified into four main categories by the International Engineering Society of North America (IESNA) based on the ability of the pavement material to reflect light (El-Rayes and Hyari 2005a). These pavement reflectance characteristics are used to determine the luminance of the pave- ment. The importance of pavement luminance stems from the fact that the sensation of glare depends on the amount of veiling luminance experienced relative to the level of luminance the eyes adapt to when exposed to this veiling luminance (in other words, the pavement luminance). To calculate the glare produced by lighting arrangements, the following three parameters need consideration: ⢠Observer positions. ⢠Pavement luminance at possible observer positions. ⢠Veiling luminance at each observer position. These positions and lines of sight are used to calculate glare and thereby determine the maxi- mum glare for all positions. This maximum computed glare is the measure used to determine the suitability of work-zone lighting arrangements (El-Rayes and Hyari 2005a). The calculation of the amount of glare experienced by drivers because of work-zone lighting arrangements starts by determining the likely positions of the drivers and their lines of sight. These positions are determined based on traffic lanes and the expected height from the ground to the driversâ eyes. This height is expected to vary based on the type of vehicle. The determination of possible driver positions and lines of sight is followed by measuring the pavement luminance Figure 3.2. Luminance meter (El-Rayes et al. 2007).
18 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity experienced by drivers at these positions or locations using the luminance meter as explained in the previous sections. Tip Glare can be decreased by increasing pavement luminance (by increasing background light- ing). This decreased glare is achieved by increasing the lighting ahead of the work zone. Key Take-Aways Glare is the ratio of veiling luminance (amount of light falling on the observerâs eyes) to pave- ment luminance (amount of light reflected off pavement surfaces). Pavement luminance can be measured using the luminance meter at a number of targets on the pavement in view of the observer (possible driver of a car passing through the work zone). Vertical luminance, on the other hand, can be measured using an illuminance meter held vertically at the same height as the observerâs eyes. Tip Increasing the mounting height of the lighting equipment in a work zone decreases glare. This means extending the mast of light towers higher or having higher poles for fixing lights on construction equipment. The trade-off in doing so to decrease glare is that the increased height decreases horizontal illuminance. Recommended Lighting Levels A major problem with nighttime work-zone lighting arrangements is the insufficiency of the lighting provided to perform the construction or maintenance task. The level of lighting needed for specific construction activities depends on factors related to the humans perform- ing the activities, as well as factors relating to the task at hand and the environment in which it takes place. For example, visual ability is a human factor that is known to vary among workers. There- fore, lighting standards assume reasonable visual abilities that are considered to be normal, while giving some allowance for variations among individuals. This assumption allows for visual standards to be based mainly on the visual requirements of the specific tasks construc- tion activities entail. Table 3.1 provides task-dependent visual standards (Ellis 2001). Table 3.1. Task-dependent visual standards (Ellis 2001). Task Dependency Visual Standard Required Accuracy The higher the precision required in a task, the higher the level of illumination needed. Background Reflection The ability to visualize an object or a target depends on the contrast between that object and the background. Highly reflective backgrounds decrease the visibility of the target or object. Relative Speed The relative speed of the object/target or its observer is another factor directly affecting the level of lighting needed for the construction task. Faster moving objects/targets necessitate higher levels of illumination. Object Size The size of the target observed in construction tasks has an impact on the needed level of illumination for the task. The smaller the object, the higher the level of lighting needed. Seeing Distance The distance between the observer and the target in each task is another determining factor in setting illumination levels. Larger distances necessitate higher levels of illumination.
Illumination 19 The above-described factors have been used to determine illumination standards in a num- ber of industries. Table 3.2 presents the levels of illumination necessary for major construction activities. Key Take-Aways ⢠Recommended illumination levels vary by task. ⢠Tasks requiring higher levels of precision need higher levels of lighting. ⢠A minimum illuminance of 54 lux needs to be maintained in general working areas for the safety of workers and the driving public. Tip One indication of the adequacy of the levels of illuminance is what could be termed the âno flashlight rule.â If the illuminance provided by the lighting equipment on the job is sufficient, field personnel should not need to use a flashlight for additional lighting in a work zone. Lighting Specifications A number of STAs have developed good temporary lighting specifications for nighttime highway construction and maintenance activities. Following is a review of some standard specifications. Illinois The Illinois Department of Transportation (IDOT) has conducted a number of studies on the appropriate lighting levels for nighttime construction work zones. That work is reflected in their standard specifications that provide details of lighting levels for specific operations. The example in Figure 3.3 specifically addresses the lighting needs for flaggers in nighttime work zones. The IDOT standard specification does not provide details for the methods used to provide such lighting levels. As a result, the special provision shown in Figure 3.4 was developed based on Lighting Category Minimum Illumination (lx) Area to be Illuminated Type of Work Activity Sample Activities I 54 Illumination throughout the work area General work area lighting, and performance of visual tasks of large size, or medium contrast, or low required accuracy Excavation Sweeping General lighting of all work areas and movement areas between tasks II 108 Illumination of work area and areas adjacent to equipment Performance of visual tasks of medium size, or low to medium contrast, or medium required accuracy Paving Milling Work areas for the active paving operation III 216 Illumination of task Performance of visual tasks of small size, or low contrast, or high required accuracy, or fine finish Crack filling Signalization systems Lighting applied directly to the task Note: lx is the symbol for lux. Table 3.2. Required illumination levels for highway construction activities (Ellis 2001).
20 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity IDOT Standard Specifications, Section 701.13 âFlaggers:â For nighttime flagging, flaggers shall be illuminated by an overhead light source providing a minimum vertical illuminance of 10 fc (108 lux) measured 1 ft (300 mm) out from the flaggerâs chest. The bottom of any luminaire shall be a minimum of 10 ft (3 m) above the pavement. Luminaire(s) shall be shielded to minimize glare to approaching traffic and trespass light to adjoining properties. Figure 3.3. Sample lighting specifications for flaggers in nighttime work zones (IDOT 2002). Nighttime Work Zone Lighting: Effective: November 1, 2008 Description. This work shall consist of furnishing, installing, maintaining, moving, and removing lighting for nighttime work zones. Nighttime shall be defined as occurring shortly before sunset until after sunrise. Materials. The lighting shall consist of mobile and/or stationary lighting systems as required herein for the specific type of construction. Mobile lighting systems shall consist of luminaires attached to construction equipment or moveable carts. Stationary lighting systems shall consist of roadway luminaires mounted on temporary poles or trailer mounted light towers at fixed locations. Some lighting systems, such as balloon lights, may be adapted to both mobile and stationary applications. Equipment. The Contractor shall furnish an illuminance meter for use by the Engineer. The meter shall have a digital display calibrated to NIST standards, shall be cosine and color corrected, and shall have an accuracy of ± five percent. The sensor shall have a level indicator to ensure measurements are taken in a horizontal plane. CONSTRUCTION REQUIREMENTS General. At the preconstruction conference, the Contractor shall submit the type(s) of lighting system to be used and the locations of all devices. Before nighttime construction may begin, the lighting system shall be demonstrated as being operational. Nighttime Flagging. The requirements for nighttime flagging shall be according to Article 701.13 of the Standard Specifications and the glare control requirements contained herein. Lighting System Design. The lighting system shall be designed to meet the following. (a) Lighting Levels. The lighting system shall provide a minimum of 5 foot candles (54 lux) throughout the work area. For mobile operations, the work area shall be defined as 25 ft (9 m) in front of and behind moving equipment. For stationary operations, the work area shall be defined as the entire area where work is being performed. Lighting levels will be measured with an illuminance meter. Readings will be taken in a horizontal plane 3 ft (1 m) above the pavement or ground surface. (b) Glare Control. The lighting system shall be designed and operated so as to avoid glare that interferes with traffic, workers, or inspection personnel. Lighting systems with flood, spot, or stadium type luminaires shall be aimed downward at the work and rotated outward no greater than 30 degrees from nadir (straight down). Balloon lights shall be positioned at least 12 ft (3.6 m) above the roadway. As a large component of glare, the headlights of construction vehicles and equipment shall not be operated within the work zone except as allowed for specific construction operations. Headlights shall never be used when facing oncoming traffic. (c) Light Trespass. The lighting system shall be designed to effectively light the work area without spilling over to adjoining property. When, in the opinion of the Engineer, the lighting is disturbing adjoining property, the Contractor shall modify the lighting arrangement or add hardware to shield the light trespass. Construction Operations. The lighting design required above shall be provided at any location where construction equipment is operating or workers are present on foot. When multiple operations are being carried on simultaneously, lighting shall be provided at each separate work area. The lighting requirements for specific construction operations shall be as follows. (a) Installation or Removal of Work Zone Traffic Control. The required lighting level shall be provided at each truck and piece of equipment used during the installation or removal of work zone traffic control. Headlights may be operated in the work zone. (b) Milling and Paving. The required lighting level shall be provided by mounting a minimum of one balloon light to each piece of mobile construction equipment used in the work zone. This would include milling machines, mechanical sweepers, material transfer devices, spreading and finishing machines, and rollers; but not include trucks used to transport materials and personnel or other vehicles that are continuously moving in and out of the work zone. The headlights of construction equipment shall not be operated within the work zone. (c) Patching. The required lighting level shall be provided at each patching location where work is being performed. (d) Pavement Marking and Raised Reflective Pavement Marker Removal/Installation. The striping truck and the attenuator/arrow board trucks may by operated by headlights alone; however, additional lighting may be necessary for the operator of the striping truck to perform the work. For raised reflective pavement marker removal and installation and other pavement marking operations where workers are on foot, the required lighting level shall be provided at each truck and piece of equipment. (e) Layout, Testing, and Inspection. The required lighting level shall be provided or each active area of construction layout, material testing, and inspection. The work area shall be defined as 15 ft (7.6 m) in front and back of the individual(s) performing the tasks. Basis of Payment. This work will be paid for at the contract lump sum price for NIGHTTIME WORK ZONE LIGHTING. Figure 3.4. Sample lighting specifications for nighttime work zones (IDOT 2008).
Illumination 21 two studies IDOT commissioned: Nighttime ConstructionâEvaluation of Lighting for Highway Construction Operations in Illinois (Report No. ITRC FR 00/01-2) and Nighttime Constructionâ Evaluation of Lighting Glare for Highway Construction in Illinois (Pub. No. FHWA-ICT-08-014). Florida The Florida Department of Transportation (FDOT) has a slightly more detailed nighttime construction lighting specification. The FDOT specification contains definitive illumination levels that should be achieved and specifies possible lighting equipment that could be used to achieve appropriate lighting levels, as shown in Figure 3.5 New Jersey The New Jersey Department of Transportation (NJDOT) has an article addressing lighting levels in the General Provisions of its Standard Specifications for Road and Bridge Construction (2007a) as shown in Figure 3.6. The levels of illuminance required are shown in Table 3.3. In addition, the NJDOT provision has a number of requirements concerning worker visibility during nighttime construction, as shown in Figure 3.7. Standard Specifications for Road and Bridge Construction 2010 Section 8-4.1 Night Work: During active nighttim e operations, furnish, place and maintain lighting sufficient to permit proper workmanship and inspection. Use lighting with 5 ft-cd minimum intensity. Arrange the lighting to prevent interference with traffic or produce undue glare to property owners. Operate such lighting only during active nighttime construction activities. Provide a light meter to demonstrate that the minimum light intensity is being maintained. Lighting may be accomplished by the use of portable floodlights, standard equipment lights, existing street lights, temporary street lights, or other lighting methods approved by the Engineer. Submit a lighting plan at the Preconstruction Conference for review and acceptance by the Engineer. Submit the plan on standard size plan sheets (not larger than 24 by 36 in.), and o n a scale of either 100 or 50 ft to 1 in. Do not start night wor k prior to the Engineerâs acceptance of the lighting plan. During active nighttime operations, furnish, place and maintain variable message signs to alert approaching motorists of lighted construction zones ahead. Operate the variable message signs only during active construction activities . Include compensation for lighting for night work in the Contract prices for the various items of the Contract. Take ownership of all lighting equipment for night work. Figure 3.5. Sample lighting specifications for road and bridge construction (FDOT 2010). 108.06 Night Operations Night operations comprises work performed from 30 minutes before sunset to 30 minutes after sunrise. Before beginning night operations, demonstrate to the Resident Engineer (RE) the method of meeting the specified illuminance levels and visibility requirements for workers and equipment for each planned operation. The Department will determine illuminance levels by taking light meter readings horizontally to the road surface facing the light source. Do not begin night operations until the RE approves the method of meeting the specified illuminance levels and visibility requirements. Figure 3.6. Sample lighting specifications for road and bridge construction (NJDOT 2007a).
22 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Work Description Minimum Level (ft candles) Minimum Lighting Area Embankment Excavation Landscaping (seeding and sodding) Mechanical sweeping and cleaning Subgrade 5 General lighting throughout area of operation Traffic control setup and removal (excluding barrier curb) 5 Lighting on task Traffic director 5 Lighting on task plus minimum of 50 ft ahead and 50 ft behind employee Milling HMA paving operation* HMA roller operation* 10 Lighting on task and around equipment plus minimum of 25 ft ahead and 25 ft behind equipment plus 10 ft to each side of equipment Crack sealing Sawcutting and sealing joints Electrical work Intelligent transportation system work 20 Lighting on task All work not listed in this table* 10 Lighting on task * Provide 5 ft candles for the indicated lighting area outside the limits for 10 ft candles to a minimum of 100 ft ahead and 100 ft behind equipment. Table 3.3. Sample illuminance-level requirements by work description (NJDOT 2007a). Visibility Requirements for Workers and Equipment: ⢠Ensure that workers wear a 360 degree high-visibility retroreflective safety garment meeting ANSI/ISEA Class 3, Level 2 standards. ⢠Uniformly light the hopper, auger, and screed areas of pavers as well as the operatorâs controls on all machines. ⢠Conventional vehicle headlights do not meet illuminance requirements. Ensure that moving lighting equipment used for night operations has lights directed ahead and behind the equipment. ⢠Equip moving equipment with two-inch wide, alternating red and white, conspicuity tape meeting the National Highway Transportation Safety Administration standards. Equip off-road equipment with conspicuity tape along the full length of all four sides. Equip on-road vehicles, including trailers and trailer-mounted devices, with conspicuity tape along the full length of both sides, excluding the cab, and across the rear of the vehicle. ⢠Prevent or minimize glare that may interfere with traffic or disturb local residents. Perform glare control to the [Resident Engineerâs] satisfaction. Glare control may require relocating, aiming, or adjusting lights or providing screens, shields, visors, or louvers on lights. Figure 3.7. Sample worker visibility specifications (NJDOT 2007a). New York The New York State Department of Transportation (NYSDOT) standard specifications for portable work-zone illumination are among the most comprehensive, as shown in Figures 3.8a and 3.8b. Types of Lighting Equipment Lighting equipment is in constant development as technologies advance at a very rapid pace. These are the four main types of lighting equipment used traditionally for nighttime work zones: light towers, balloon lighting, Night Lite, and high-mast lighting.
Illumination 23 NEW YORK STATE DEPARTMENT OF TRANSPORTATION STANDARD SPECIFICATIONS as of May 1, 2008 619-3.19 Nighttime Operations. A. Nighttime Operations and Lighting Plan. Thirty days prior to the start of nighttime operations, the Contractor shall submit a written Nighttime Operations and Lighting Plan to the Engineer for approval. The plan shall detail all aspects of the traffic control setup, the functions, responsibilities and identities of the traffic control supervisor and other details as necessary. It shall include a contingency plan identifying foreseeable problems and emergencies that may arise, and the approach that will be used to address them. This plan shall be revised and updated by the Contractor as necessary during the progress of the work to accommodate conditions on the contract. The Contractor shall submit a Nighttime Operations and Lighting Plan to the Engineer, at a scale and printed size similar to the contract plans and appropriate to adequately describe the work, including the following: Layout showing location of light towers, including typical spacing, lateral placement and mounting height, and clearly show the location of all lights necessary for all work to be done at night. Description of light towers to be used and electrical power source. Specific technical details on all lighting equipment, including brand names, model numbers, power rating and photometric data. Details of any hoods, louvers, shields or other means to be used to control glare. Attachment and mounting details for lights to be attached to equipment. Lighting calculations confirming that the illumination requirements will be met by the layout. The Contractor shall maintain a supply of emergency flares for use in the event of unanticipated situations such as traffic accidents, equipment breakdowns, failure of lighting equipment, etc. B. Lighting for Nighttime Operations. Prior to the first night of nighttime operations, the Contractor shall set up and operate the lighting equipment at night as a trial run to demonstrate its ability to establish a safe, properly illuminated, nighttime operation. The Contractor shall furnish the Engineer with a photometer, capable of measuring the level of illumination, for use as necessary to check the adequacy of illumination throughout nighttime operations. 1. Equipment. The Contractor shall supply all lighting equipment required to provide a work zone safe for the workers and traffic. Material and/or equipment shall be in good operating condition and in compliance with applicable safety and design codes. a. Light Towers. Light towers shall be provided as a primary means of illumination, and shall provide Level I illumination throughout the work space. They may be supplemented to the extent necessary by lighting fixtures mounted on construction equipment to provide Level II or Level III illumination where required for paving, milling and similar moving operations. Light towers shall be sturdy and free-standing without the aid of guy wires or bracing, and shall be capable of being moved as necessary to keep pace with construction operations. Light towers shall be positioned to minimize the risk of being impacted by traffic on the roadway or by construction traffic or equipment. b. Light Towers on Paving, Milling, and Finishing Machines. If needed to supplement portable and/or trailer-mounted light towers, towers shall be affixed to paving, milling, and finishing machines to provide the required level of illumination for the specified distance in front of and behind the machine. No portion of machine-mounted light towers shall exceed a height of 13 ft above ground. Luminaires shall be aimed and adjusted to provide uniform illumination with a maximum uniformity ratio of 5:1. The hopper, auger, and screed areas of pavers and the operatorâs controls on all machines shall be uniformly illuminated. c. Construction Equipment Lights. All construction equipment, including rollers, backhoes, loaders, and other equipment operating in areas not illuminated to a minimum of Level I Illumination, shall be equipped with a minimum of two 500 watt flood lights facing in each direction to provide a minimum of 1 foot-candles of horizontal illumination measured 60 ft in front of and behind the equipment. In areas illuminated to a minimum of Level I, construction equipment may move unescorted. In non-illuminated areas, construction equipment shall be equipped with conventional vehicle headlights, shall be illuminated with flood lights on the vehicle, or shall be escorted to permit safe movement. Headlights shall not be permitted as the sole means of illumination while working. Figure 3.8a. Sample nighttime operations specifications page 1 (NYSDOT 2008). Light Towers Light towers are one of the most commonly used types of portable lighting equipment (see Figure 3.9). Light towers typically have a power generator, a retractable mast, and two to six lighting fixtures. All of these components are mounted on a trailer that can be towed by a construction vehicle.
24 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity d. Equipment Mounting. The Contractor shall provide suitable brackets and hardware to mount lighting fixtures and generators on machines and equipment. Mountings shall be designed so that light fixtures can be aimed and positioned as necessary to reduce glare and to provide the required illumination. Mounting brackets and fixtures shall not interfere with the equipment operator or any overhead structures, and shall provide for secure connection of the fixtures with minimum vibration. e. Portable Generators. The Contractor shall provide portable generators to furnish adequate power to operate all required lighting equipment. Fuel tank capacity and availability of fuel on site shall be sufficient to permit uninterrupted operation throughout the planned shift. Adequate switches shall be provided to control the various lights. All wiring shall be weatherproof and installed in accordance with 29 CFR 1926 Subpart K requirements. All power sources shall be equipped with a Ground-Fault Circuit Interrupter. 2. Illumination Requirements. Tower-mounted luminaires, whether fixed, portable, trailer mounted, or equipment-mounted, shall be of sufficient wattage and/or quantity to provide the required level of illumination and uniformity over the area of operation. The uniformity of illumination, defined as the ratio of the average illumination to the minimum illumination over an area requiring an indicated illumination level, shall not exceed 5:1. Illumination levels on approach roadways should be increased sequentially to prevent motorists from becoming disoriented by rapid changes from full dark to very bright conditions. Existing street and highway lighting shall not eliminate the need for the Contractor to provide lighting. Consideration will be given to the amount of illumination provided by existing lights in determining the wattage and/or quantity of lights to be provided. Such consideration shall be presented in the Contractorâs Nighttime Operations and Lighting Plan. In the event of any failure of the lighting system, nighttime operation(s) shall be discontinued until the required level of illumination is restored. a. Level I (5 foot-candles). Level I illumination shall be provided for all areas of general construction operations to include all work operations by Contractorsâ personnel, including work zone traffic control set-up and operations, staging, excavation, cleaning and sweeping, spoil disposal, landscaping, planting and seeding, layout and measurements ahead of the actual work, borrow areas, spoil areas, and truck cleanout areas. Level I illumination shall be provided at the area of lane and/or road closure tapers continuously, including the setup and removal of the closure tapers. Level I illumination shall be provided a minimum of 400 ft ahead and 800 ft behind a paving or milling machine, or for the entire area of concrete placement or pavement work if less than 1,500 ft. This area shall be extended as necessary to incorporate all vehicle and equipment operations associated with the paving operation. The only exception to the requirement for Level I illumination throughout the area of construction operations is that finish rollers can work beyond the area of Level I illumination using floodlights mounted on the roller. b. Level II (10 foot-candles). Level II illumination shall be provided for flagging stations, asphalt paving, milling, and concrete placement and/or removal operations, including bridge decks, 50 ft ahead and 100 ft behind a paving or milling machine. c. Level III (20 foot-candles). Level III illumination shall be provided for pavement or structural crack filling, joint repair, pavement patching and repairs, installation of signal equipment or other electrical/mechanical equipment, and other tasks involving fine details or intricate parts and equipment. 3. Glare Control. All lighting shall be designed, installed, and operated to avoid glare that affects traffic on the roadway or that causes annoyance or discomfort for residences adjoining the roadway. The Contractor shall locate and aim lighting fixtures to provide the required level of illumination and uniformity in the work zone without the creation of objectionable glare. The Engineer will determine when glare exceeds acceptable levels, either for traffic or for adjoining residences. The Contractor shall provide shields, visors or louvers on luminaires as necessary to reduce objectionable levels of glare. As a minimum, the following requirements shall be met to avoid objectionable glare on roadways open to traffic in either direction: ⢠Tower-mounted luminaires shall be aimed either generally parallel or perpendicular to the roadway. ⢠Luminaires shall be aimed such that the angle between the center of the beam axis and the vertical mounting pole is no greater than 45E. ⢠No luminaires shall be permitted that provide a luminous intensity greater than 20,000 candelas at an angle of 72E above the vertical. ⢠Except where prevented by overhead utilities or structures, towers shall be extended to their full working height when in use to reduce glare and provide uniform illumination. Figure 3.8b. Sample nighttime operations specifications page 2 (NYSDOT 2008). The luminaires installed in light towers are usually fitted with 1,000 to 1,500 watt metal halide, high-pressure sodium, or tungsten halogen bulbs. Different bulbs vary in the color of their light and in the time it takes for them to warm up (Gambatese 2005). Light towers have a number of features that increase their versatility and flexibility in lighting outdoor space. The retractable masts can be raised to 30 ft and rotate 360 degrees around their ver- tical axis. These towers can light areas ranging from five to seven acres using only four luminaires.
Illumination 25 Balloon Lighting Balloon lights are intended for use as equipment-mounted lights or in stationary locations such as flagger stations (Figure 3.10). These lights have fabric covers that are inflated with air or helium and they can be mounted on stands. The source of light enclosed in the fabric cover is either a halogen bulb or a Hydrargyrum Medium-arc Iodide (HMI) system. Balloon lights can illuminate spaces ranging from 108,000 to 432,000 sq ft. The main advantages of balloon lighting are that it distributes light over 360 degrees, offers glare-free lighting, and can be mounted as high as 164 ft (Gambatese 2005). Nite Lite A new equipment type that was utilized in an IDOT test was the Nite Lite (see Figure 3.11). The Nite Lite was a portable light composed of a 400-watt metal halide lamp in a dome-shaped casing coated with a light-diffusing material. The luminaire had a weight of 11.8 kg, and the dome had a diameter of 0.635 m. Figure 3.9. Typical light tower (El-Rayes et al. 2007).
26 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity The luminaire was powered by a 120-volt AC source that could produce up to 42,000 lumens, which could provide lighting for an area of 1,395 sq m (El-Rayes et al. 2007). High-Mast Lighting The fourth type of construction lighting is a semi-permanent lighting system for the illu- mination of work zones. High-mast lighting systems are composed of luminaires mounted on high-mast poles. These were first used by the NYSDOT in 2005 for a three-mile stretch of I-90 at Albany, New York (see Figure 3.12) (Freyssinier et al. 2008). The system was proposed as an alternative for portable light towers. The photo shows this test section and the high-mast lighting system. Table 3.4 shows the main characteristics of high-mast lighting systems, including the hori- zontal illuminance produced. The measurements were taken in conditions that had no ambient background lighting and followed IESNA measurement guidelines. The average illuminance the system produces is more than 100 lux, which is sufficient for the movement of construction workers and some construction activities such as pavement resurfac- ing (Freyssinier et al. 2008). The results of the evaluation of the systemâs performance showed that it met lighting qual- ity specifications for nighttime work zones. The comparison of the performance of high-mast lighting to portable light towers showed it provided sufficient illumination with fewer shadows and relatively low glare. Figure 3.10. Balloon lights (El-Rayes et al. 2007).
Illumination 27 Figure 3.11. Nite Lite lighting equipment (El-Rayes et al. 2007). Figure 3.12. Test stretch for high-mast lighting (Freyssinier et al. 2008, photo Dennis Guyon, Lighting Research Center).
28 A Guidebook for Nighttime Construction: Impacts on Safety, Quality, and Productivity Key Take-Aways ⢠Light towers are the most common type of construction lighting equipment. Light towers are suitable for lighting large stationary areas. ⢠Balloon lights are used for lighting small to medium stationary areas or can be equipment- mounted. ⢠High-mast lighting is a new type of lighting that is semi-permanent in nature. Tip Agencies do not usually prescribe the lighting equipment used by contractors to provide appropriate lighting levels. Therefore, most contractors select lighting equipment based on avail- ability and price. These criteria may not result in equipment that results in optimum lighting arrangements. Therefore, attention should be given to contractor-submitted lighting plans and proposed equipment. Resource IESNA pavement reflectance categories can be found in the American National Standards Institute (ANSI)/IESNA RP-8-00 report, which is available online at http://www.scribd.com/ doc/38492536/Ansi-Iesna-Rp-8-00. Category/Item Value Photometric Characteristics Total number of pole locations 108 Mounting height 70 ft Typical pole spacing (staggered layout) 320 ft between poles on same side of road Number of luminaires per pole 4 Total number of luminaires 432 Lamp type per luminaire Metal halide, 1,500 W Lamp life 7,000 to 8,000 h Predicted Illuminance on Pavement (Software Calculation) Average 133 lx Maximum 233 lx Minimum 80 lx Average to minimum ratio 3.0:1 Maximum to minimum ratio 2.9:1 Actual Illuminance on Pavement (Measure on Site) Average 148 lx Maximum 209 lx Minimum 101 lx Average to minimum ratio 1.5:1 Maximum to minimum ratio 2.1:1 Electrical Characteristics Input power per luminaire 1,564 W Total installed load for lighting 675.6 kW Number of generators installed 5 Total power available per generator 250 kW Total installed generation capacity 1,250 kW Table 3.4. Lighting properties of high-mast lighting systems (Freyssinier et al. 2008).
