CLD Lighting Fundamentals 4 — Questions and Answers
Question 1: What is the spectral power distribution (SPD) of a light source?
- The total power consumed by the source in watts
- A graph showing radiant power emitted at each wavelength across the visible spectrum (Correct answer)
- The ratio of visible to infrared radiation emitted
- The efficiency of a source measured in lumens per watt
Correct answer: A graph showing radiant power emitted at each wavelength across the visible spectrum
An SPD curve shows how the radiant power of a light source is distributed across each wavelength of the visible (and adjacent) spectrum.
Question 2: A retail display luminaire is specified with a narrow beam angle. What effect does this have on the target?
- Lower center-beam candlepower and broader coverage
- Higher center-beam candlepower and concentrated illuminance (Correct answer)
- Lower efficacy and higher heat generation
- Wider beam spread and reduced shadowing
Correct answer: Higher center-beam candlepower and concentrated illuminance
A narrower beam angle concentrates luminous intensity into a smaller solid angle, resulting in higher center-beam candlepower and more focused, high illuminance on the target.
Question 3: What is 'adaptation' in the context of the human visual system?
- The eye's ability to discriminate between fine details
- The process by which the eye adjusts its sensitivity to different luminance levels (Correct answer)
- The perception of color under varying spectral conditions
- The automatic adjustment of depth perception in dim light
Correct answer: The process by which the eye adjusts its sensitivity to different luminance levels
Visual adaptation is the process by which the eye adjusts its sensitivity (via pupil dilation and photoreceptor response) to match prevailing luminance conditions.
Question 4: In lighting design, what does 'task-ambient ratio' refer to?
- The ratio of task illuminance to general (ambient) illuminance in a space (Correct answer)
- The difference in color temperature between task and ambient luminaires
- The power density of task lighting versus total connected load
- The ratio of direct to indirect luminaire output
Correct answer: The ratio of task illuminance to general (ambient) illuminance in a space
The task-ambient ratio compares the illuminance level on the work surface to the surrounding ambient light level, affecting visual comfort and energy efficiency.
Question 5: Which of the following best describes 'photopic luminosity function' (V(λ))?
- The spectral sensitivity of the human eye under dark-adapted (scotopic) conditions
- The spectral sensitivity of the human eye under bright (photopic) conditions, peaking near 555 nm (Correct answer)
- The total radiant power across all wavelengths emitted by a blackbody radiator
- The luminance distribution of a perfectly diffuse surface under daylight
Correct answer: The spectral sensitivity of the human eye under bright (photopic) conditions, peaking near 555 nm
The photopic luminosity function V(λ) describes the relative sensitivity of the light-adapted human eye to different wavelengths, peaking at approximately 555 nm (green-yellow).
Question 6: What is 'sky component' (SC) in daylight factor calculations?
- Light reaching a point directly from the sky vault without obstruction (Correct answer)
- Light reflected from the ground before entering the window
- Light reflected from interior room surfaces
- The portion of daylight blocked by window glazing tint
Correct answer: Light reaching a point directly from the sky vault without obstruction
The sky component (SC) is the portion of daylight factor attributable to light arriving directly from the sky vault without any surface reflections.
Question 7: What happens to the color appearance of a light source as its correlated color temperature (CCT) increases from 3000K to 6500K?
- It shifts from cool blue-white to warm amber
- It shifts from warm amber to cool blue-white (Correct answer)
- It shifts from green to red
- It remains neutral white regardless of CCT change
Correct answer: It shifts from warm amber to cool blue-white
As CCT increases, the light source shifts from warm amber tones (low CCT ~2700–3000K) toward neutral white and then a cool blue-white (high CCT ~5000–6500K).
CLD Lighting Fundamentals 4
What is the spectral power distribution (SPD) of a light source?