IMSA Roadway Lighting II flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Luminous flux

Total light output emitted by a source in all directions, measured in lumens (lm). Luminaire lumen output is the basis for illuminance calculations and efficacy comparisons.

Illuminance

Light arriving at a surface per unit area, expressed in lux (lm/m²) or footcandles. One footcandle equals about 10.76 lux. Horizontal illuminance is used for roadway design criteria.

Luminance

Light reflected or emitted from a surface in a given direction, measured in candela per square meter (cd/m²). Roadway luminance and its uniformity drive driver visibility and comfort.

Coefficient of utilization

Fraction of luminaire lamp lumens that reaches the roadway surface, depending on luminaire distribution, mounting height, geometry, and surface reflectances. Used in the lumen method.

Light loss factor

Product of lamp lumen depreciation, luminaire dirt depreciation, ballast or driver factor, and ambient factors. Converts initial lumens to maintained lumens for design calculations.

Mesopic vision

Vision state at intermediate light levels where both rod and cone photoreceptors contribute. Higher correlated color temperature sources can improve perceived brightness at equal photopic luminance.

Veiling luminance ratio

Ratio of maximum veiling luminance from glare to average roadway luminance. Standards cap this ratio to limit disability glare, with stricter limits at higher design speeds.

Luminance uniformity ratio

Ratio of maximum to minimum (or average to minimum) roadway luminance. Uniformity limits prevent alternating bright and dark patches that impair driver detection.

IES roadway classification

Categories such as freeway, arterial, collector, and local road that set design criteria. Higher speed and volume classifications require higher luminance and stricter uniformity.

BUG rating

Backlight, uplight, and glare rating system for outdoor luminaires. Local ordinances use BUG ratings to limit light trespass, skyglow, and glare.

NEC Article 410

National Electrical Code article covering luminaires, lamp holders, and associated equipment. It sets installation, support, and wiring requirements but does not set photometric design levels.

Warrant analysis

Study of roadway classification, traffic volume, pedestrian activity, and nighttime crash history to decide whether lighting is justified. Results support funding and design decisions.

LED driver

Power supply converting AC line voltage to regulated constant current for LED modules. Output current, forward voltage range, dimming protocol, and programming must match the luminaire.

L70 lumen maintenance

Projected operating hours when LED lumen output falls to 70 percent of initial. Values are extrapolated using TM-21 methods from measured LM-80 data.

High-pressure sodium lamp

Arc discharge source with high efficacy and warm orange light. Requires a ballast with ignitor and capacitor; its low color rendering limits use where color matters.

Ballast factor

Ratio of lamp lumens produced on a given ballast to lumens on a reference ballast. It scales both light output and input power in fluorescent and HID systems.

IES distribution type

Luminaire light pattern classification from Type I (narrow, along roadway) to Type V (symmetric). Type and cutoff classification determine spacing and glare control.

IP rating

Ingress protection code giving resistance to dust and water, such as IP65 or IP66. It indicates suitability of luminaire and driver enclosures for outdoor roadway environments.

Effective projected area

Wind-facing area of luminaire and arm, used with wind pressure to compute pole loads. Manufacturer EPA values feed structural calculations for poles and foundations.

Anchor bolt circle

Pattern diameter and count of anchor bolts matching the pole base plate. Bolt projection, embedment, and torque must follow the pole manufacturer's drawings.

Breakaway transformer base

Frangiible pole base designed to yield on vehicle impact, reducing crash severity. Commonly required near high-speed traffic where fixed poles pose a hazard.

Pole base moment

Bending moment at the pole base equal to wind force times lever arm. It governs foundation size, anchor bolt design, and pole wall thickness selection.

Direct-buried pole

Pole set into soil without a concrete foundation, relying on embedment depth and soil resistance. Soil type, compaction, and groundwater affect overturning capacity.

Voltage drop formula

Single-phase two-wire: VD = 2 x I x R x L. Three-phase: VD = 1.732 x I x R x L. R is conductor resistance per unit length; L is one-way length.

Series lighting circuit

Constant-current loop feeding luminaires through isolation transformers. The regulator maintains current; opening the loop under load is hazardous and requires fault protection.

Photocell control

Sensor switching lighting at dusk and dawn. It typically operates a contactor coil so the contactor, not the photocell, carries full circuit current.

Inrush current

Brief high current when drivers or ballasts energize. Breakers and contactors must be sized with inrush in mind to prevent nuisance tripping on lighting circuits.

Equipment grounding conductor

Conductor bonding non-current-carrying metal parts to ground. It provides a low-impedance fault path and is required for poles and luminaires by the NEC.

Adaptive lighting controls

Networked systems that dim or schedule roadway lighting by time or traffic level. They report faults and energy use, and can reduce output during low-traffic hours.

Lockout tagout

Procedure isolating and locking energy sources before maintenance. Required for lighting circuit work; verify absence of voltage before touching conductors.

Photometric field verification

Measuring illuminance with a calibrated meter at grid points after installation. Results are compared with design criteria to confirm the system meets specification.

MUTCD temporary traffic control

Manual guidance for work-zone traffic control, including signs, cones, and flaggers. Roadway lighting maintenance near traffic must follow these layouts for worker safety.