NCQLP LC flashcards
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33 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Illuminance
- Luminous flux incident on a unit area of surface, measured in lux (lm/m²) or footcandles (lm/ft²). It is the quantity most codes and IES recommendations specify for tasks.
- Luminance
- Luminous intensity emitted or reflected per unit projected area, in cd/m². It corresponds to perceived brightness and is the quantity that produces glare and visibility contrast.
- Inverse-square law
- Illuminance from a point source equals intensity divided by the square of the distance, E = I/d². Doubling the distance reduces illuminance to one quarter of its prior value.
- Cosine law
- Illuminance on a tilted surface equals I·cosθ/d², where θ is the angle between the incoming light and the surface normal. Off-axis light delivers proportionally less illuminance.
- Luminous efficacy
- Ratio of luminous flux produced to electrical power consumed, in lumens per watt. It allows comparison of source efficiency, though system efficacy should include driver and ballast losses.
- Correlated color temperature
- The absolute temperature of a blackbody whose color appearance most closely matches the lamp, in kelvin. Warm sources are below about 3300 K; cool sources exceed 5300 K.
- Color rendering index
- A 0–100 scale comparing a source's rendering of test color samples with a reference source. Higher values indicate more faithful color appearance; R9 specifically rates saturated red.
- Maintenance factor
- A multiplier below one accounting for lumen depreciation, dirt on luminaires and surfaces, and lamp failures. Design illuminance equals initial illuminance multiplied by this factor.
- Coefficient of utilization
- The fraction of lamp lumens that reaches the work plane, derived from luminaire photometrics, room cavity ratio, and surface reflectances. Higher values mean more efficient delivery.
- Room cavity ratio
- A dimensionless index of room proportions used with photometric tables: RCR = 5·h·(L+W)/(L·W), where h is cavity height. Larger values indicate taller or narrower rooms.
- Lumen method
- The average-illuminance design formula: number of luminaires = (target illuminance × area) ÷ (lumens per lamp × coefficient of utilization × maintenance factor). It assumes uniform layout.
- Spacing-to-mounting-height ratio
- The maximum luminaire spacing divided by mounting height above the work plane that still yields acceptable uniformity. Exceeding the rated value causes scalloping and dark bands.
- Lighting power density
- Connected lighting watts divided by floor area, in W/m² or W/ft². Energy codes set maximum allowances by space type; controls and reduced wattage help comply.
- LENI
- Lighting energy numeric indicator, total annual lighting energy divided by floor area in kWh/m²/yr. Unlike power density, it reflects operating hours and control savings.
- L70 rating
- The operating hours at which a population of LED luminaires is projected to reach 70 percent of initial lumen output. It is a statistical depreciation rating, not a failure guarantee.
- Ballast factor
- The ratio of a lamp's light output on a given ballast to its output on the reference ballast. It scales both lumens and input wattage in fluorescent calculations.
- UGR
- Unified glare rating, a scale for discomfort glare from interior luminaires. Lower values mean less glare; office tasks commonly specify limits such as 19 or lower.
- BUG rating
- Backlight, uplight, and glare ratings that summarize an outdoor luminaire's light distribution. They are used to control light trespass, skyglow, and glare at property lines.
- Occupancy sensor
- A control that turns lighting on when presence is detected and off after a set delay. Vacancy sensors instead require manual-on operation, which typically saves more energy.
- Daylight harvesting
- Automatic dimming or stepped switching of electric lighting in response to available daylight, using a photosensor. Proper calibration prevents hunting and nuisance switching.
- Veiling reflection
- Reflected glare that reduces task contrast, often seen on glossy paper or screens. It is addressed by relocating or shielding the source rather than raising illuminance.
- Cylindrical illuminance
- Average illuminance on the vertical surface of a small cylinder at a point. It indicates how well faces and vertical surfaces are lit in a space.
- Flicker index
- A measure of light output modulation above the average, ranging from 0 to 1. Higher values indicate more perceptible flicker and potential stroboscopic effects.
- IES photometric file
- A digital file describing a luminaire's intensity distribution, lumen output, and spacing criteria. Calculations are only valid if the file matches the installed luminaire and optic.
- Footcandle
- One lumen of luminous flux incident on one square foot of surface, equal to about 10.76 lux. It is still used in many US lighting recommendations and codes.
- Lux
- One lumen of luminous flux incident on one square meter of surface. It is the SI unit of illuminance and the basis for most metric lighting design targets.
- Simple payback
- Installed retrofit cost divided by annual energy and maintenance savings. It is a quick screening metric that ignores energy escalation and equipment life beyond the payback period.
- Egress illumination
- Minimum lighting along the path of egress, commonly about 10.8 lux (1 fc) at floor level, maintained for 90 minutes on emergency power. Exit signs must also be illuminated.
- Commissioning
- Verification that installed lighting and controls meet design intent: measured illuminance, calibrated sensors, confirmed sequences, and documented settings handed to the owner.
- SDCM
- Standard deviation of color matching, a measure of color consistency between lamps. A small value such as 3–5 means adjacent luminaires appear nearly identical in tint.
- Task-ambient lighting
- A strategy using modest general ambient light plus localized task lighting at work surfaces. It reduces total connected load while maintaining adequate task illuminance and contrast.
- Light trespass
- Spill light falling beyond the property boundary or into unwanted areas. It is limited by full cut-off optics, aiming, shielding, and backlight ratings on outdoor luminaires.
- Luminous flux
- The total light output of a source in all directions, measured in lumens. Lamp and luminaire lumen ratings are the starting point for any illuminance calculation.