IMSA Roadway Lighting I flashcards
IMSA Roadway Lighting I · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Illuminance
- Luminous flux incident per unit area on a surface, measured in lux (lm/m²) or footcandles (lm/ft²); 1 fc equals 10.76 lux.
- Luminance
- Luminous intensity per unit projected area in a given direction, measured in cd/m²; roadway visibility design is based on luminance rather than illuminance.
- Inverse-square law
- Illuminance from a point source equals intensity divided by distance squared; at an angle from nadir, E = I(θ)·cos³θ/h² for mounting height h.
- Veiling luminance ratio
- The ratio of maximum veiling luminance to average roadway luminance; it quantifies disability glare from luminaires toward the observer and is a design criterion.
- Maintained illuminance
- Design illuminance after applying lamp lumen depreciation and luminaire dirt depreciation to initial values; calculations must use maintained, not initial, photometric values.
- Lumen depreciation (LLD)
- The fraction of initial lamp or luminaire lumen output remaining at end of life or at a specified time; used as a multiplier in maintained illuminance calculations.
- Luminaire dirt depreciation (LDD)
- The fraction of light output remaining after dirt accumulates on the luminaire; depends on environment category and luminaire design, and multiplies with LLD.
- Correlated color temperature
- The absolute temperature of a blackbody whose chromaticity most closely matches the light source, measured in kelvin; warmer sources have lower CCT.
- Color rendering index
- A 0-100 scale describing how faithfully a light source renders object colors compared with a reference source; higher values indicate better color fidelity.
- Roadway design classification
- The category assigned to a roadway based on functional class, pedestrian conflict level, and area type; it determines the applicable luminance, uniformity, and glare criteria.
- Spacing-to-mounting-height ratio
- The ratio of pole spacing to luminaire mounting height; it influences luminance uniformity and typically ranges from about 3:1 to 5:1 for roadway lighting.
- Luminaire overhang
- The horizontal distance a luminaire extends beyond the curb face toward the roadway; it reduces house-side spill and improves roadway-side uniformity.
- Luminaire setback
- The horizontal distance from the curb face to the luminaire's vertical axis; it affects spill control and the effective roadway-side light distribution.
- Full cutoff luminaire
- A luminaire that emits no light at or above 90 degrees from nadir and limits intensity in the 80-90 degree zone, reducing glare and skyglow.
- BUG rating
- A three-part rating (backlight, uplight, glare) from IES TM-15 describing a luminaire's zonal lumen distribution and its light trespass and skyglow characteristics.
- IES LM-63 file
- The standard electronic photometric file format containing a luminaire's intensity distribution, lumen output, and metadata for use in design software.
- Pole overturning moment
- The bending moment at the pole base from wind, ice, and luminaire loads; it governs foundation and anchor bolt design.
- Voltage drop
- The reduction in voltage along a conductor due to resistance; for a single-phase two-wire circuit, V_drop = 2·L·I·R, and it is commonly limited to about 3% on branch circuits.
- Photocell control
- A device that switches luminaires on at dusk and off at dawn based on ambient light level; large loads may use a contactor controlled by the photocell.
- Luminance meter
- A calibrated instrument that measures luminance in a specific direction; field measurements are typically taken from about 1.45 m eye height and 83 m ahead.
- Lamp seasoning
- Operating HID lamps for about 100 hours before photometric measurement to stabilize output; LED luminaires generally do not require the same seasoning.
- LM-79 report
- A photometric test report for an LED luminaire giving absolute lumen output, efficacy, CCT, CRI, and intensity distribution for the complete luminaire.
- Adaptive lighting
- A control strategy that reduces luminaire output during low-traffic periods while still meeting the reduced criteria applicable to the reduced traffic volume.
- 0-10 V dimming
- A common analog dimming interface for LED drivers using a low-voltage control signal; verify the driver's minimum dimming level and compatibility with the controller.
- Light trespass
- Light that falls beyond the property boundary; it is often limited by ordinance in terms of vertical illuminance at the property line.
- Skyglow
- Upward-directed light that brightens the night sky; it is reduced by full-cutoff luminaires with low uplight ratings and warmer CCT where permitted.
- Luminaire schedule
- A construction document table listing each luminaire type with manufacturer, model, lumen output, CCT, CRI, BUG rating, voltage, and mounting accessories.
- Point-by-point calculation report
- A document recording the software used, grid spacing, observer position, maintenance factors, and resulting average, minimum, and uniformity values for a lighting design.
- Disability glare
- Glare that reduces visual performance and contrast sensitivity by adding veiling luminance to the observer's field of view.
- Discomfort glare
- Glare that causes annoyance or discomfort without necessarily reducing visibility; it is influenced by luminaire brightness and the observer's adaptation level.
- Life-cycle cost
- The present value of initial capital, energy, maintenance, and disposal costs over an asset's life; used to compare lighting design alternatives on a total-cost basis.
- TM-21 projection
- A method for projecting LED lumen maintenance beyond LM-80 test duration, limited to six times the test duration and dependent on drive current and temperature.