IMSA Roadway Lighting I cheat sheet

Illuminance (E) is luminous flux incident per unit area, measured in lux (lm/m²) or footcandles (lm/ft²); 1 fc = 10.76 lux.

Luminance (L) is reflected or emitted intensity per unit projected area in the observer's direction, measured in cd/m²; roadway visibility design is based on luminance, not illuminance.

Luminous intensity (I) in candela equals flux per solid angle (cd = lm/sr); a luminaire's distribution is published as an isocandela diagram or I-table.

Inverse-square law: E = I/d² for a point source at perpendicular incidence; at an angle θ from nadir, E = I(θ)·cos³θ/h² where h is mounting height.

Uniformity ratios: max-to-min (E_max/E_min) and max-to-average (E_max/E_avg); average-to-minimum (E_avg/E_min) is used in luminance-based design.

Veiling luminance ratio (L_vmax/L_avg) limits disability glare; it is computed from luminaire intensity toward the observer and the observer's eye adaptation level.

Lamp metrics that matter: luminous efficacy (lm/W), correlated color temperature (CCT), color rendering index (CRI), lumen depreciation (LLD), and luminaire dirt depreciation (LDD).

Maintained values = initial value × LLD × LDD; design calculations must use maintained illuminance/luminance, not initial photometric values.

IES RP-8 is the primary recommended-practice document for roadway and street lighting design criteria; IES LM-79 covers electrical/photometric measurement and LM-80 covers lumen maintenance testing.

Roadway lighting design categories are set by road functional class, pedestrian conflict level, and area classification (commercial, intermediate, residential).

Design criteria tables give average maintained luminance, uniformity ratios, veiling luminance ratio, and sometimes average illuminance for each roadway classification.

Pole spacing-to-mounting-height ratio (S/H) typically ranges from about 3:1 to 5:1 for luminance uniformity; larger ratios generally degrade uniformity.

Standard luminaire arrangements: one-side, staggered/opposite, twin/median-mounted, and central/mast-arm; one-side suits narrow roads with S/H near 3, opposite suits wide roads.

Mounting height selection balances glare control (higher is better), uniformity, and spill light; typical street lighting heights run from about 7.5 m to 12 m for major roads.

Overhang (luminaire offset beyond the curb) reduces house-side spill and improves roadway-side uniformity; excessive overhang wastes light behind the pole line.

Setback is the horizontal distance from the curb face to the luminaire's vertical axis; it affects both spill control and the effective roadway-side distribution.

Luminaire classification uses cutoff categories (full cutoff, cutoff, semi-cutoff, non-cutoff) based on the intensity emitted at and above 90° and 80° from nadir.

B U G ratings (backlight, uplight, glare) from IES TM-15 describe luminaire light trespass and skyglow characteristics and are often referenced in local ordinances.

Luminaire photometric files use the IES LM-63 (.ies) format, containing lumen output, intensity distribution, and CCT/CRI metadata; verify the file matches the actual product configuration.

A luminaire's BUG rating is derived from its zonal lumen sums: backlight (B0-B5), uplight (U0-U5), and glare (G0-G5).

Pole foundations are designed from the pole's overturning moment, which combines luminaire and bracket weight, wind load on the pole and luminaire, and ice load where applicable.

Wind load calculation uses the design wind pressure times the projected area of the pole and luminaire, applied at the appropriate height above the foundation.

Anchor bolts, base plates, and handhole orientation must be coordinated with the pole manufacturer's shop drawings and the structural engineer's foundation design.

Voltage drop in branch circuits must be checked: V_drop = 2·L·I·R per conductor for single-phase two-wire; keep within the local code or utility limit (commonly 3% on branch circuits).

Luminaire circuits are typically protected by a photocell or time clock for dusk-to-dawn control, with contactors for large loads.

Electrical service and grounding must comply with the adopted electrical code (e.g., NEC Article 410 for luminaires and Article 250 for grounding) and any local amendments.

Field measurement of illuminance uses a calibrated meter with cosine and color correction, held horizontally at the roadway surface and at the specified grid points.

Luminance measurement uses a calibrated luminance meter aimed along the observer's line of sight, typically from a point 1.45 m above the roadway and about 83 m ahead.

Measurement grid spacing depends on roadway width and mounting height; points are usually taken at the center of each grid cell, avoiding the immediate pole base.

Maintained illuminance is verified by comparing field readings to the design values after applying LLD and LDD, accounting for lamp seasoning and dirt on the lens.

Lamp seasoning: HID lamps are typically operated about 100 hours before photometric measurement to stabilize output; LED luminaires generally do not require the same seasoning.

Photometric testing per LM-79 reports absolute photometry for LED luminaires (lumens and efficacy directly), unlike traditional lamps tested separately from the luminaire.

Commissioning checks include verification of photocell operation, circuit voltage at the luminaire, correct aiming/orientation, and absence of visible flicker or color shift.

As-built documentation should record actual mounting heights, pole locations, luminaire model and lumen setting, and measured illuminance/luminance values.

Adaptive lighting controls dim luminaires during low-traffic periods; design must still meet the reduced criteria applicable to the reduced traffic volume.

LED luminaires offer dimming via 0-10 V, DALI, or proprietary protocols; verify compatibility between the driver, controller, and network.

Networked lighting controls can provide scheduling, photocell-based dimming, fault monitoring, and energy reporting; commissioning must verify each node's address and profile.

Energy code compliance (e.g., ASHRAE 90.1 or local amendments) may cap lighting power density for exterior lighting; controls can be a compliance path.

Light trespass limits are often set by local ordinance in terms of vertical illuminance at the property line; verify the luminaire's backlight distribution and aiming.

Skyglow reduction favors full-cutoff luminaires with low uplight (U0) ratings and warmer CCT where the local ordinance permits.

Retrofit economics compare LED wattage, lumen output, and controls savings against existing HID systems; include maintenance savings from longer life.

Maintenance planning should account for group relamping or driver replacement intervals and access equipment needs for high-mast or median-mounted poles.

Roadway lighting design is typically delivered as a plan-and-profile sheet showing pole locations, mounting heights, and luminaire schedule.

The luminaire schedule lists type, manufacturer, model, lumen output, CCT, CRI, BUG rating, voltage, and mounting accessories.

The photometric layout plan shows calculated illuminance or luminance contours overlaid on the roadway, with the design criteria stated in a table.

A point-by-point calculation report documents the software used, grid spacing, observer position, maintenance factors, and the resulting average, max, min, and uniformity values.

Coordination is required with the roadway geometric design (curb lines, shoulders, clear zones) so poles do not become fixed-object hazards.

Clear-zone and breakaway requirements: poles within the clear zone should be breakaway or shielded, per the applicable roadside design guide.

Utility coordination is needed for service points, metering, and any conflict with existing overhead or underground facilities.

Specifications should reference the applicable IES test standards (LM-79, LM-80, TM-21) and require submittal of photometric files and test reports.

Glare is quantified by veiling luminance (L_v) added to the observer's field; the ratio L_vmax/L_avg is a common design criterion.

Disability glare reduces contrast and visibility; discomfort glare causes annoyance without necessarily reducing visibility.

Trespass light is measured as vertical illuminance at the property line, often at 1.5 m above grade, and is limited by local ordinance.

Skyglow is upward-directed light; full-cutoff luminaires with U0 uplight ratings minimize it.

Light pollution ordinances often combine BUG rating limits, CCT limits, and curfew dimming requirements.

Tunnel and underpass lighting requires transition zones to manage adaptation between daylight and interior lighting levels.

Pedestrian-scale lighting at crosswalks and transit stops uses lower mounting heights and vertical illuminance criteria for facial recognition.

Glare from oncoming luminaires can be mitigated by shielding, reduced intensity at high angles, and proper mounting height and setback.

Life-cycle cost includes initial capital, energy, maintenance (lamps, drivers, labor, equipment), and disposal; present-worth analysis discounts future costs.

LED luminaires typically have longer rated life (e.g., 50,000+ hours to L70 or L80) than HID lamps, reducing relamping frequency and labor cost.

Lumen maintenance for LED is projected using TM-21 from LM-80 test data; the reported L70/L80/L90 values depend on drive current and temperature.

Energy savings depend on wattage reduction, controls-based dimming, and reduced losses; calculate annual kWh from connected wattage times operating hours.

Utility rebates and demand-side programs may offset capital cost; verify eligibility requirements such as DLC listing or specific lumen/watt thresholds.

Maintenance factors for LED systems differ from HID because lumen depreciation and dirt depreciation curves differ; use manufacturer-provided LLD and LDD data.

Group relamping strategies for HID systems reduce labor cost per lamp compared with spot relamping.

Total cost of ownership comparisons should normalize for maintained lumens, not initial lumens, to avoid overstating one technology's performance.

Safety and liability: lighting design should follow recognized recommended practices (IES RP-8) to demonstrate a reasonable standard of care.

Photometric calculations must be reproducible; retain software files, input assumptions, and output reports for the project record.

Field verification should confirm that installed luminaires match the specified photometric file and that aiming and orientation are correct.

Any substitution of luminaires requires recalculation to confirm the design criteria are still met.

Documentation of maintenance factors and assumed lamp/luminaire depreciation should be explicit in the design report.

Inspection checklists should cover foundation, pole plumbness, anchor bolt torque, handhole orientation, grounding, and luminaire aim.

Punch-list items commonly include misaimed luminaires, incorrect photocell settings, damaged finishes, and missing labels.

Record drawings should reflect as-installed conditions and be delivered with operation and maintenance manuals.

Roadway lighting design software computes point-by-point illuminance and luminance using luminaire photometric files and roadway geometry.

Inputs include mounting height, overhang, setback, spacing, arrangement, luminaire tilt, maintenance factors, and observer position.

Outputs include average and minimum illuminance/luminance, uniformity ratios, veiling luminance ratio, and contour plots.

Grid spacing should be fine enough to capture the minimum values; coarse grids can overstate uniformity.

Observer position for luminance calculations is typically 1.45 m eye height and 83 m ahead of the calculation area, per RP-8 conventions.

Verify that the photometric file's coordinate system and units match the software's expectations (feet vs. meters, type C vs. type B).

Sensitivity checks: vary maintenance factor, spacing, and mounting height to see how robust the design is to field conditions.

Results should be compared against the design criteria table for the roadway classification before the design is finalized.

Poles are specified by material (steel, aluminum, concrete, fiberglass), height, shaft taper, wall thickness, and finish.

Anchor bolts and base plates must match the pole manufacturer's template; verify bolt circle, diameter, and projection.

Breakaway or slip-base poles are used in clear zones to reduce collision severity; they must meet the applicable breakaway requirements.

Pole grounding: a grounding electrode at each pole, bonded to the equipment grounding conductor, is commonly required by the electrical code.

Handholes should face away from traffic and be at a consistent height for maintenance access.

Luminaire mounting accessories include brackets, tenons, davit arms, and trunnion mounts; verify arm length and rise match the photometric design.

Pole finish (galvanized, painted, anodized) affects corrosion resistance and maintenance; specify per environment (coastal, industrial).

Shop drawing review should confirm dimensions, material certifications, and compatibility with the specified luminaire.

Roadway lighting design begins with classifying the road by functional class, pedestrian conflict, and area type, then selecting the corresponding design criteria.

Select luminaire photometric data and mounting height; check that the S/H ratio supports the required uniformity.

Choose an arrangement (one-side, opposite, staggered, median) based on road width and available pole locations.

Run point-by-point calculations using maintained values; iterate on spacing, mounting height, and overhang until criteria are met.

Check glare criteria (veiling luminance ratio) and light trespass limits in addition to illuminance/luminance.

Coordinate with structures, utilities, and clear zones; adjust pole locations as needed and re-verify calculations.

Prepare the luminaire schedule, layout plan, and calculation report; specify testing and submittal requirements.

Review submittals and shop drawings against the design; perform field verification after installation.

IES LM-79 covers electrical and photometric measurements of LED luminaires; results are absolute (lumens, efficacy, CCT, CRI) for the complete luminaire.

IES LM-80 covers lumen maintenance and color maintenance testing of LED packages, arrays, and modules at specified case temperatures.

IES TM-21 projects lumen maintenance beyond LM-80 test duration; projections are limited to 6× the test duration.

IES LM-63 defines the electronic photometric file format (.ies) used by design software.

IES TM-15 defines the BUG rating system for luminaires based on zonal lumen distributions.

IES RP-8 provides recommended practice for roadway and street lighting design criteria and calculation methods.

IES RP-20 addresses parking facility lighting; IES RP-33 addresses lighting for exterior environments including trespass and skyglow.

ANSI C136 series covers luminaire testing and performance standards; verify the specific standard referenced in the specification.

HID lamps (high-pressure sodium, metal halide) require warm-up and restrike time; HPS has high efficacy but poor CRI, metal halide has better CRI but shorter life.

LED luminaires offer instant-on, dimmability, long life, and high efficacy; thermal management is critical to maintaining rated life and lumen output.

Fluorescent sources are rarely used for roadway lighting due to low output and cold-weather performance.

Induction lamps have long life but lower efficacy than LED and limited dimming capability.

Color metrics: CCT describes apparent color (warm to cool), CRI describes color rendering fidelity (0-100).

Lumen depreciation curves differ by source; HID lamps depreciate significantly, while LED depreciation is gradual and temperature-dependent.

Driver lifetime for LED is often the limiting factor; specify drivers with appropriate surge protection and thermal design.

Compatibility of dimming controls with drivers must be verified; not all 0-10 V drivers dim to the same minimum level.

Light trespass ordinances commonly limit vertical illuminance at the property line and may also limit luminaire backlight (B) ratings.

Skyglow ordinances favor full-cutoff luminaires, low uplight (U0), and sometimes warmer CCT limits.

Curfew dimming requirements may mandate reduced output after a specified hour; verify the control system supports the required dimming profile.

Some jurisdictions require shielded luminaires near residential areas or dark-sky preserves.

Compliance documentation may require photometric calculations showing property-line illuminance and BUG ratings.

Ordinance requirements can conflict with design criteria; resolve by adjusting mounting height, aiming, or luminaire selection.

Verify the current version of the local ordinance; requirements change and may reference specific IES standards.

Environmental review may require assessment of impacts on wildlife and dark-sky resources.

Project delivery includes design, specification, bidding, submittal review, construction observation, and closeout.

Submittals should include luminaire cut sheets, photometric files, LM-79 reports, LM-80/TM-21 data, and pole shop drawings.

Substitution requests require recalculation and comparison against the specified performance criteria.

Construction observation should verify pole locations, mounting heights, luminaire aim, and electrical connections.

Commissioning verifies controls operation, photocell settings, dimming profiles, and network connectivity.

Closeout documents include as-builts, O&M manuals, warranties, and training records.

Warranty terms should cover luminaire, driver, finish, and pole; verify duration and exclusions.

Punch-list resolution should be documented and verified before final acceptance.

Energy calculations: annual kWh = connected watts × operating hours / 1000; include controls savings from dimming schedules.

Demand charges may apply to roadway lighting circuits; verify with the utility rate schedule.

Lighting power density limits for exterior lighting may apply under energy codes; controls can provide a compliance path.

Utility rebates often require DLC listing, minimum efficacy, and controls; document eligibility before bidding.

Maintenance cost estimates should include lamp/driver replacement, labor, equipment, and disposal.

Life-cycle cost analysis discounts future costs to present value using an appropriate discount rate.

Payback period = initial incremental cost / annual savings; simple payback ignores discounting.

Sensitivity analysis on energy prices and maintenance intervals improves the reliability of the economic comparison.

Roadway lighting design must consider the roadway geometry: number of lanes, median width, curvature, and intersection locations.

Intersections require higher illuminance and uniformity than midblock sections due to conflict points.

Crosswalks and pedestrian areas require vertical illuminance for facial recognition and conflict detection.

Roundabouts require lighting of the circulatory roadway and approach legs; glare control is important for drivers entering.

Tunnels and underpasses require transition lighting to manage adaptation; design must consider daytime and nighttime conditions.

Bridges may have restrictions on pole mounting and require coordination with the bridge designer.

Work zone lighting must maintain safe illuminance while minimizing glare to workers and drivers.

Parking facilities and transit stops have their own recommended practices (RP-20 and related).

Maintenance factors for roadway lighting include lamp lumen depreciation (LLD) and luminaire dirt depreciation (LDD); maintained = initial × LLD × LDD.

LED lumen maintenance is projected using TM-21 from LM-80 data; the projection depends on drive current and temperature.

Dirt depreciation depends on environment (clean, moderate, dirty) and luminaire design (sealed vs. open).

Group relamping reduces labor cost per lamp but may replace lamps before end of life; spot relamping reduces waste but increases labor.

Maintenance schedules should account for access equipment and traffic control costs.

Field measurements should be taken after lamp seasoning and cleaning to compare against maintained design values.

Record keeping of failures and relamping dates supports predictive maintenance.

Warranty claims require documentation of installation conditions and operating hours.

Electrical design includes service entrance, branch circuits, voltage drop, grounding, and overcurrent protection.

Voltage drop limits are commonly 3% on branch circuits and 5% total; verify against the adopted code and utility requirements.

Grounding and bonding must comply with the electrical code; each pole typically requires a grounding electrode conductor.

Photocell and time clock control circuits should be coordinated with contactors for large loads.

Surge protection is recommended for LED luminaires, especially in areas with frequent lightning.

Circuit loading must account for inrush current of LED drivers and HID ballasts.

Conductor sizing must consider ambient temperature, conduit fill, and derating factors.

As-built electrical drawings should show circuit assignments, panel schedules, and control settings.

Roadway lighting design criteria are organized by roadway classification: freeway, major, collector, local, and pedestrian facilities.

Each classification has recommended average maintained luminance, uniformity ratios, and veiling luminance limits.

Pedestrian conflict levels (high, medium, low) modify the criteria for a given roadway class.

Area classification (commercial, intermediate, residential) further refines the criteria.

Some jurisdictions use illuminance-based criteria instead of luminance-based; verify the adopted standard.

Adaptive lighting allows reduced criteria during low-traffic periods; the reduced criteria must be documented.

Design criteria should be stated explicitly in the calculation report and compared against results.

When criteria conflict between documents, the more stringent applicable requirement generally governs unless the authority having jurisdiction directs otherwise.

Quality assurance during construction includes inspection of foundations, pole erection, and luminaire installation.

Foundation inspection verifies dimensions, reinforcement, anchor bolt placement, and concrete strength.

Pole erection inspection verifies plumbness, anchor bolt torque, and handhole orientation.

Luminaire inspection verifies model, lumen setting, aim, and orientation against the design.

Electrical inspection verifies grounding, circuit continuity, voltage, and control operation.

Nonconformance should be documented and resolved before acceptance.

Testing records should include photometric measurements where required by the specification.

Final acceptance should be contingent on resolution of all punch-list items.

Roadway lighting design must consider the visual task: drivers detect obstacles, pedestrians, and other vehicles against the roadway background.

Luminance contrast between an object and its background determines visibility; higher contrast improves detection.

Small target visibility (STV) is an alternative design method that weights visibility of small targets across the roadway.

Adaptation level affects visibility; bright surroundings reduce contrast sensitivity.

Glare reduces visibility by adding veiling luminance to the field of view.

Pedestrian visibility depends on vertical illuminance and contrast against the background.

Design should consider both daytime and nighttime conditions where applicable.

Visibility-based design may be appropriate where luminance-based criteria are not sufficient.

Pole spacing is determined by the required uniformity and the luminaire's distribution; S/H ratios commonly range from 3 to 5.

Mounting height affects both uniformity and glare; higher mounting heights improve uniformity but may increase spill light.

Overhang and setback affect the distribution of light on the roadway and the amount of spill behind the pole line.

Luminaire tilt changes the photometric distribution and should match the manufacturer's tested configuration.

Median-mounted luminaires can light both roadway directions but may require taller poles and careful glare control.

Twin-arm luminaires on median poles can be cost-effective for wide roadways.

Spacing should be checked against the calculated uniformity, not just the S/H rule of thumb.

Field adjustments to aim or tilt require recalculation to confirm criteria are still met.

Roadway lighting design should consider sustainability: energy efficiency, longevity, and recyclability of components.

LED luminaires generally have higher efficacy and longer life than HID, reducing energy and maintenance impacts.

Dark-sky friendly design reduces skyglow and ecological impacts.

Life-cycle assessment can compare environmental impacts of design alternatives.

Disposal of lamps and drivers must comply with applicable regulations (e.g., mercury-containing lamps).

Reducing light trespass improves neighbor acceptance and may be required by ordinance.

Controls that dim during low-use periods reduce energy consumption.

Specifying repairable luminaires extends service life and reduces waste.

Roadway lighting design software typically supports point-by-point calculations for illuminance and luminance.

Input geometry includes roadway width, lane configuration, curb lines, and median.

Luminaire input includes photometric file, mounting height, overhang, setback, tilt, and maintenance factor.

Observer position for luminance calculations is typically 1.45 m eye height and 83 m ahead.

Grid spacing should be fine enough to capture minimum values; verify convergence by refining the grid.

Results should be exported and included in the design report with all input assumptions.

Software version and photometric file names should be recorded for reproducibility.

Sensitivity analysis helps identify which inputs most affect the results.

Roadway lighting specifications should reference applicable IES standards for testing and performance.

Specifications should require submittal of photometric files and test reports for verification.

Luminaire specifications should include lumen output, CCT, CRI, BUG rating, voltage, and dimming protocol.

Pole specifications should include material, height, finish, anchor bolt details, and breakaway requirements.

Installation specifications should cover foundation construction, pole erection, and luminaire aiming.

Testing and commissioning requirements should be stated explicitly.

Warranty requirements should cover luminaire, driver, finish, and pole.

Substitution procedures should require recalculation and comparison against the specified criteria.

Roadway lighting design must coordinate with the roadway geometric design to avoid poles in clear zones.

Poles within the clear zone should be breakaway or shielded per the applicable roadside design guide.

Coordination with utilities is required for service points and conflicts with existing facilities.

Coordination with structures is required for bridge-mounted or building-mounted luminaires.

Coordination with landscaping is required to avoid conflicts with trees and to prevent light blockage.

Coordination with pedestrian facilities ensures adequate lighting at crosswalks and transit stops.

Coordination with traffic signals and signage avoids conflicts and ensures visibility.

Coordination with the authority having jurisdiction is required for permits and approvals.

Roadway lighting design should be documented with a design report that states criteria, assumptions, and results.

The report should include the luminaire schedule, layout plan, and calculation output.

Maintenance factors and their basis should be documented.

Software inputs and photometric file names should be recorded for reproducibility.

Deviations from recommended practice should be justified and documented.

The report should be reviewed and sealed by the responsible professional where required.

As-built documentation should reflect any changes made during construction.

Records should be retained per project and jurisdictional requirements.

Roadway lighting design should consider the needs of all road users, including drivers, pedestrians, and cyclists.

Pedestrian crossings require vertical illuminance for facial recognition and conflict detection.

Bicycle facilities may require lighting that reveals surface hazards and other users.

Transit stops require lighting for waiting passengers and security.

Accessible design considerations include lighting of ramps, stairs, and signage.

Glare control is important for all users, especially pedestrians and cyclists who may be more sensitive.

Lighting should be consistent along a route to avoid dark gaps.

Community input may inform design decisions in residential areas.

Roadway lighting design must consider the visual environment: background luminance, signage, and adjacent lighting.

Bright adjacent areas (e.g., commercial signage) can increase adaptation level and reduce visibility.

Dark surroundings can cause discomfort glare from luminaires.

Transition zones between bright and dark areas require gradual changes in illuminance.

Tunnel lighting design requires careful management of adaptation.

Lighting of intersections should consider the approach lighting from each direction.

Lighting of curves may require closer spacing or different aiming.

Lighting of hills and grades may require adjustment of mounting height and aiming.

Roadway lighting design should consider the maintenance access: poles should be accessible for bucket trucks or other equipment.

Median-mounted poles may require special access considerations.

High-mast lighting requires specialized access equipment and maintenance procedures.

Handholes should be oriented for safe access away from traffic.

Maintenance schedules should account for traffic control costs.

Spare parts should be stocked for critical components.

Training for maintenance staff should cover safe access and proper procedures.

Maintenance records should be kept for warranty and planning purposes.