IMSA Roadway Lighting II cheat sheet

Luminous flux is measured in lumens (lm); illuminance in lux (lm/m²) or footcandles (1 fc = 10.76 lux); luminance in cd/m².

Luminous intensity (candela, cd) describes flux per solid angle; a luminaire's distribution is reported as a polar intensity curve in cd per 1000 lm.

Illuminance (horizontal or vertical) supports small-object/pedestrian detection; luminance and its uniformity govern driver comfort and visibility on higher-speed roadways.

Average maintained illuminance = (lamp lumens × luminaire count × CU × LLF) / area, where CU is coefficient of utilization and LLF is light loss factor.

Luminance uniformity metrics: average-to-minimum ratio (max/min) and maximum-to-minimum ratio; longitudinal uniformity is measured along the driver's line of sight.

Lamp lumens depreciate and luminaires accumulate dirt; LLF = LLD × LDD × other factors (ballast/driver factor, ambient temperature factor).

Correlated color temperature (CCT) in kelvin describes apparent whiteness; color rendering index (CRI) rates fidelity of object colors under the source.

Glare types: disability glare reduces visibility (veiling luminance), discomfort glare causes annoyance; both are controlled by luminaire shielding and mounting height.

Mesopic vision applies at typical roadway luminance levels; higher-CCT sources can appear brighter at equal photopic luminance, affecting perceived visibility.

Design criteria for roadways typically specify average maintained illuminance or luminance, uniformity ratios, veiling luminance ratio, and glare control by luminaire classification.

Roadway classifications commonly used: freeway, major/multi-lane arterial, minor arterial, collector, local/residential; criteria tighten as speed and traffic volume increase.

Design method choices: illuminance method for pedestrian-conflict and low-speed areas; luminance method for higher-speed vehicular roadways.

Veiling luminance ratio (max veiling luminance to average roadway luminance) limits discomfort/disability glare; thresholds are stricter for higher design speeds.

Warranted lighting is often triggered by a warrant analysis combining roadway classification, pedestrian volume, and nighttime crash history.

The National Electrical Code (NFPA 70) governs installation requirements; Article 410 covers luminaires, and Article 411 covers low-voltage lighting systems.

The NEC does not set photometric design levels; photometric criteria come from standards such as IES/ANSI recommended practice documents and local agency specifications.

Accessibility and dark-sky/light-trespass ordinances may cap uplight, backlight, and glare ratings (e.g., BUG ratings) and require full cut-off optics.

Design deliverables typically include photometric calculation reports, luminaire schedules, voltage drop calculations, and pole/foundation structural submittals.

Common roadway sources: high-pressure sodium (HPS, ~90-150 lm/W, warm orange), metal halide, induction, and LED (often 100-160 lm/W system efficacy).

LED luminaires use constant-current drivers; driver output is rated in mA and forward voltage range must match the LED module string.

LED luminaire ratings include luminaire efficacy (lm/W), lumen maintenance (e.g., L70, L80, L90 hours), and TM-21 projected life.

Driver programming (0-10 V, DALI, or proprietary) sets output current and dimming curve; incorrect programming changes lumens and power.

HPS and metal halide require ballasts: magnetic (core-and-coil, with capacitor and ignitor for HPS) or electronic; ballast factor scales lamp lumens.

Pulse-start metal halide needs an ignitor and has hot-restrike limitations; probe-start lamps differ in starting circuit requirements.

LED optics are classified by IESNA distribution types (Type I, II, III, IV, V) and cutoff classifications (full cut-off, cut-off, semi-cut-off, non-cut-off).

Ingress protection (IP) ratings and ANSI/UL listings (e.g., UL 1598 for luminaires, UL 8750 for LED equipment) define environmental suitability.

Dimming and controls compatibility: 0-10 V analog, DALI digital, or line-voltage step dimming; verify driver dimming range and standby power.

Design wind loads per ASCE 7 use basic wind speed, exposure category, height/gust factors, and the luminaire's effective projected area (EPA).

Pole loading combines luminaire EPA, arm EPA, and pole drag; total moment at the base = force × lever arm (height above base).

Pole materials: steel (galvanized or weathering), aluminum, fiberglass/composite, and concrete; each has different strength and corrosion behavior.

Anchor-bolt foundations: bolt circle, bolt projection, and embedment must match the pole base; torque values come from the pole manufacturer.

Direct-buried poles rely on soil bearing and embedment depth; soil type and compaction affect overturning resistance.

Breakaway or frangible transformer bases are used in high-speed/high-risk areas to reduce vehicle impact severity.

Handhole covers and grounding lugs must remain accessible; pole grounding conductor sized per NEC Article 250 and local utility requirements.

Pole height, arm length, and luminaire tilt set the mounting height and luminaire spacing used in photometric calculations; verify as-built geometry.

Vibration and fatigue considerations include vortex shedding; dampers or tuned mass devices may be required on tall or slender poles.

Voltage drop on a circuit: single-phase two-wire VD = 2 × I × R × L; three-phase VD = √3 × I × R × L, with R in ohms per unit length.

Common distribution voltages for roadway lighting: 120/240 V single-phase, 240/480 V, and series circuits at higher voltage with constant-current regulators.

Series lighting circuits use a constant-current regulator and isolation transformers at each luminaire; open-circuit protection is required.

Conductor sizing considers ampacity per NEC 310, terminals rated 75°C, and voltage drop limits often set at 3-5% by specification.

Grounding and bonding: equipment grounding conductor, pole grounding electrode, and bonding of metal parts per NEC Article 250 and 410.

Overcurrent protection and disconnecting means are required; each pole or circuit needs a readily accessible disconnect where specified.

Photocell or time-clock control enables dusk-to-dawn operation; contactors handle circuit current while photocells switch the coil.

Adaptive or networked controls (central management systems) allow dimming schedules, fault reporting, and energy metering over power-line or wireless links.

Luminaire drivers and ballasts have inrush current; account for it when sizing breakers and contactors to avoid nuisance tripping.

Pre-energization inspection: verify torque on terminations, ground continuity, insulation resistance, and correct phase/neutral connections.

Energized work requires lockout/tagout, arc-flash PPE per NFPA 70E, and qualified-person rules; de-energize whenever feasible.

Bucket truck and aerial work require fall protection, spotter/ground control, and adherence to approach distances from energized lines.

Photometric field verification uses a calibrated illuminance meter at grid points; compare maintained values against design criteria.

Lumen depreciation and dirt depreciation are managed by group relamping or scheduled cleaning; track luminaire run hours for LED L70 planning.

Fault diagnosis sequence: check source voltage, breaker/contactor state, photocell output, driver/ballast input, then luminaire output.

Ground-fault and open-circuit checks on series circuits use the regulator's fault indicators; never open a series loop under load.

Post-installation records: as-built pole locations, luminaire aiming, control settings, and test results support future maintenance and warranty claims.

Traffic control during work follows the Manual on Uniform Traffic Control Devices (MUTCD) temporary traffic control guidance.