CLD Lighting Fundamentals 3 — Questions and Answers
Question 1: What is the primary purpose of a photometric report (IES file) for a luminaire?
- To specify the lamp's color rendering index
- To document the electrical wiring diagram
- To provide candela distribution data for lighting calculations (Correct answer)
- To certify the luminaire for UL listing
Correct answer: To provide candela distribution data for lighting calculations
An IES photometric file contains the candela distribution data used by lighting software to calculate illuminance, luminance, and other metrics.
Question 2: Which of the following describes 'veiling reflections' in a lighting design?
- Specular reflections from a task surface that reduce contrast and visibility (Correct answer)
- Reflections that create pleasing highlights on decorative objects
- Light bounced off ceilings to improve uniformity
- Reflections that enhance color saturation on painted walls
Correct answer: Specular reflections from a task surface that reduce contrast and visibility
Veiling reflections are specular reflections from a task surface (e.g., glossy paper) that wash out contrast and reduce visual performance.
Question 3: What is the 'coefficient of utilization' (CU) used for in zonal cavity calculations?
- To correct illuminance values for lamp age
- To represent the fraction of lamp lumens that reach the work plane (Correct answer)
- To account for the color temperature shift of LEDs
- To calculate the maintenance factor for a luminaire
Correct answer: To represent the fraction of lamp lumens that reach the work plane
The CU represents the proportion of total lamp lumens that actually reaches the work plane, accounting for luminaire efficiency and room geometry.
Question 4: What does 'glare' in a lighting system primarily result from?
- Insufficient illuminance on the task
- Excessive luminance contrast in the visual field (Correct answer)
- Low color rendering index of the source
- High lamp efficacy at full power
Correct answer: Excessive luminance contrast in the visual field
Glare occurs when luminance contrast between a bright source or surface and its surroundings exceeds comfortable levels, causing discomfort or disability.
Question 5: What is 'mesopic vision,' and when does it occur?
- Vision under full daylight conditions using only cones
- Vision in complete darkness using only rod receptors
- Vision under intermediate light levels using both rods and cones (Correct answer)
- Vision impaired by excessive UV radiation from light sources
Correct answer: Vision under intermediate light levels using both rods and cones
Mesopic vision occurs at intermediate luminance levels (approximately 0.001 to 3 cd/m²) where both rods and cones are active.
Question 6: Which IESNA metric is used to evaluate the potential for discomfort glare from indoor luminaires?
- Unified Glare Rating (UGR)
- Visual Comfort Probability (VCP) (Correct answer)
- Daylight Glare Probability (DGP)
- Glare Rating Index (GRI)
Correct answer: Visual Comfort Probability (VCP)
Visual Comfort Probability (VCP) is the IESNA metric estimating the percentage of observers who would find a lighting installation acceptable without discomfort glare.
Question 7: What does the term 'lumen depreciation' refer to in lamp performance?
- The reduction in lamp wattage over time due to aging
- The gradual decrease in light output as a lamp ages (Correct answer)
- The loss of color rendering ability at end of life
- The drop in lamp voltage during initial warm-up
Correct answer: The gradual decrease in light output as a lamp ages
Lumen depreciation describes the reduction in luminous flux output that occurs as a lamp ages, typically expressed as a percentage of initial lumens.
CLD Lighting Fundamentals 3
What is the primary purpose of a photometric report (IES file) for a luminaire?