CLD Outdoor Lighting 4 — Questions and Answers
Question 1: A roadway lighting project requires maintained average luminance of 1.0 cd/m² at end of design life. If the initial design delivers 1.4 cd/m², what Light Loss Factor (LLF) was assumed?
- 0.56
- 0.71 (Correct answer)
- 0.86
- 1.40
Correct answer: 0.71
LLF = maintained value ÷ initial value = 1.0 ÷ 1.4 ≈ 0.71, meaning the designer accounted for ~29% depreciation over the design life.
Question 2: Which ANSI/IES standard specifically addresses outdoor sports and recreational area lighting?
- IES RP-6 (Correct answer)
- IES RP-8
- IES RP-20
- IES RP-33
Correct answer: IES RP-6
IES RP-6 'Sports and Recreational Area Lighting' provides illuminance recommendations, uniformity criteria, and glare ratings for various sports and competition levels.
Question 3: An outdoor museum facade luminaire uses a narrow-beam (10°) LED projector. Technicians report color shift across the beam at the edges. What is the most likely cause?
- Thermal derating of the LED driver
- Chromatic aberration from the lens design separating phosphor emission wavelengths at oblique angles (Correct answer)
- Incorrect CCT specified at time of purchase
- Inadequate ingress protection allowing moisture in the optic
Correct answer: Chromatic aberration from the lens design separating phosphor emission wavelengths at oblique angles
Narrow-beam lenses can exhibit chromatic aberration at the beam edge where light passes through at oblique angles, causing blue or yellow fringing from the phosphor-converted LED source.
Question 4: For a high-mast lighting installation (pole height ≥20m), which factor most significantly increases maintenance costs compared to standard-height pole lighting?
- Higher lamp replacement frequency due to vibration
- Requirement for bucket-truck or climbing access to service the luminaire head (Correct answer)
- Greater wind-load calculations increasing pole cost
- Need for higher-wattage sources reducing lamp life
Correct answer: Requirement for bucket-truck or climbing access to service the luminaire head
High-mast poles require specialized access equipment (bucket trucks or lowering rings) for maintenance, making each service visit substantially more expensive than for standard pole heights.
Question 5: A landscape architect requests 'moonlighting' for a garden. Which technique best achieves this effect?
- Uplighting trees from ground-level with cool white sources
- Mounting warm-white fixtures high in tree canopy aimed downward to cast dappled shadows (Correct answer)
- Installing blue-tinted pathway bollards at 0.5m height
- Using color-changing RGB fixtures programmed to a cool blue cycle
Correct answer: Mounting warm-white fixtures high in tree canopy aimed downward to cast dappled shadows
Moonlighting places warm-white luminaires high in tree branches angled downward, mimicking the natural appearance of moonlight filtering through a canopy and creating natural shadow patterns below.
Question 6: In the context of the IDA/IES Model Lighting Ordinance, 'Backlight-Uplight-Glare (BUG) ratings' serve which primary design function?
- Rating the energy efficiency of the luminaire driver
- Quantifying light emitted rearward, upward, and at high angles as separate zonal values for code compliance (Correct answer)
- Measuring the lamp's color rendering index under outdoor conditions
- Classifying the impact resistance of the outer housing
Correct answer: Quantifying light emitted rearward, upward, and at high angles as separate zonal values for code compliance
BUG ratings provide three separate zonal flux values — Backlight, Uplight, and Glare — allowing designers to verify MLO compliance for each emission direction independently.
Question 7: Which approach best reduces 'spill light' onto an adjacent residential property from a commercial parking lot?
- Increasing pole height to spread light more evenly
- Selecting luminaires with asymmetric Type II or III distributions aimed inward (Correct answer)
- Using higher-wattage sources with wider beam spreads
- Installing luminaires with Type V symmetric distributions
Correct answer: Selecting luminaires with asymmetric Type II or III distributions aimed inward
Asymmetric Type II or III distributions concentrate light toward the interior of the lot while limiting emission toward the property line, reducing spill onto adjacent residential properties.
CLD Outdoor Lighting 4
A roadway lighting project requires maintained average luminance of 1.0 cd/m² at end of design life.
If the initial design delivers 1.4 cd/m², what Light Loss Factor (LLF) was assumed?