CLD Outdoor Lighting 5 — Questions and Answers
Question 1: A city specifies a minimum Color Rendering Index (CRI) of 70 for new street lighting. A proposed LED fixture has CRI 72 but a poor R9 value of 10. What concern does this raise?
- The fixture will fail lumen maintenance requirements faster
- Saturated red objects such as brake lights and stop signs may appear washed out or brownish (Correct answer)
- The fixture will produce excessive blue light hazard
- The driver efficiency will be reduced below acceptable levels
Correct answer: Saturated red objects such as brake lights and stop signs may appear washed out or brownish
R9 measures rendering of saturated red; a very low R9 (even with CRI ≥ 70) means red safety-critical elements like brake lights and stop signs appear desaturated, reducing visual safety cues.
Question 2: What is 'ecological light pollution' and which wavelength range is of greatest concern for insect populations?
- Visible red light causing thermal stress in insects
- Ultraviolet and short-wavelength blue-green light attracting and disorienting insects (Correct answer)
- Infrared light disrupting insect thermoregulation
- Broad-spectrum white light reducing insect camouflage effectiveness
Correct answer: Ultraviolet and short-wavelength blue-green light attracting and disorienting insects
Insects are highly sensitive to UV and short-wavelength blue-green light (300–550nm), which attracts and disorients them around artificial light sources, disrupting feeding, mating, and predator-prey relationships.
Question 3: A designer is calculating the maintained illuminance for an outdoor walkway after 5 years. Which combination of factors comprises the overall Light Loss Factor (LLF)?
- Lamp lumen depreciation (LLD) only
- LLD × luminaire dirt depreciation (LDD) × ballast factor (BF)
- LLD × LDD × voltage variation × thermal factor (Correct answer)
- BUG rating × fixture efficacy × pole spacing
Correct answer: LLD × LDD × voltage variation × thermal factor
The comprehensive LLF includes all recoverable and non-recoverable factors: lamp lumen depreciation, luminaire dirt depreciation, voltage variation, and temperature effects on output.
Question 4: Under NFPA 70 (National Electrical Code), outdoor luminaires installed in wet locations must be listed and labeled for:
- 'Damp location' use only
- 'Wet location' use (Correct answer)
- 'Hazardous location' use
- 'Dry location' use with weatherproofing added
Correct answer: 'Wet location' use
NEC Article 410.10(A) requires luminaires exposed to weather or water to be listed specifically for wet locations; 'damp location' listings are insufficient for direct rain or water exposure.
Question 5: A sports broadcaster requests lighting for a multi-camera HD broadcast at a stadium. The primary additional photometric requirement compared to recreational play illuminance is:
- Higher Kelvin temperature (≥6500K) for camera white balance
- Increased vertical illuminance levels and uniformity to adequately illuminate players' faces and vertical surfaces for cameras (Correct answer)
- Lower horizontal illuminance to reduce glare for viewers
- A minimum CRI of 50 for camera sensor compatibility
Correct answer: Increased vertical illuminance levels and uniformity to adequately illuminate players' faces and vertical surfaces for cameras
Broadcast cameras require high vertical illuminance (not just horizontal) on player faces and vertical surfaces, with tight uniformity ratios (Emax/Emin ≤ 2.0) to avoid overexposed and underexposed zones in the frame.
Question 6: Which material property makes Type 316 stainless steel preferable to Type 304 stainless steel for coastal outdoor luminaire hardware?
- Higher tensile strength for wind load resistance
- Molybdenum content providing superior resistance to chloride (salt) corrosion (Correct answer)
- Lower thermal expansion coefficient reducing thermal cycling stress
- Better reflectivity for concealed mounting applications
Correct answer: Molybdenum content providing superior resistance to chloride (salt) corrosion
Type 316 stainless steel contains 2–3% molybdenum, which significantly improves resistance to chloride-induced pitting and crevice corrosion common in coastal salt-air environments.
Question 7: A historic district ordinance restricts luminaire height to 3.5m on a pedestrian street 6m wide. If a designer cannot meet IES RP-8 illuminance recommendations at this height, what is the most appropriate design response?
- Request a variance from IES standards to reduce required illuminance levels
- Increase spacing between poles to compensate for the reduced height
- Reduce pole spacing and potentially use opposite-side staggered or opposite-side opposing configurations to achieve coverage (Correct answer)
- Install ground-recessed uplights to supplement overhead fixtures
Correct answer: Reduce pole spacing and potentially use opposite-side staggered or opposite-side opposing configurations to achieve coverage
Reducing pole spacing and using a staggered or opposing pole layout distributes overlapping light pools more evenly, compensating for the reduced mounting height constraint.
CLD Outdoor Lighting 5
A city specifies a minimum Color Rendering Index (CRI) of 70 for new street lighting.
A proposed LED fixture has CRI 72 but a poor R9 value of 10.
What concern does this raise?