CLD Daylighting Design 5 — Questions and Answers
Question 1: A CLD candidate is asked to evaluate daylighting in an existing building. Which instrument would directly measure interior illuminance at a workplane?
- Luminance meter (spotmeter)
- Photometric goniometer
- Calibrated illuminance meter (lux meter) (Correct answer)
- Integrating sphere
Correct answer: Calibrated illuminance meter (lux meter)
A calibrated illuminance meter (lux meter) with a cosine-corrected photocell measures illuminance (lux or footcandles) at a surface, which is the standard metric for workplane daylighting evaluation.
Question 2: How does increasing the reflectance of interior ceiling and wall surfaces affect daylighting performance?
- It decreases daylight penetration depth by absorbing more light near the window
- It increases daylight levels in the interior by redirecting inter-reflected light deeper into the space (Correct answer)
- It has no measurable effect on horizontal workplane illuminance
- It primarily reduces glare by diffusing bright reflections near windows
Correct answer: It increases daylight levels in the interior by redirecting inter-reflected light deeper into the space
High-reflectance interior surfaces bounce daylight from surface to surface, increasing both the depth of daylight penetration and the overall illuminance in the space through inter-reflections.
Question 3: The solar altitude angle at which a horizontal overhang just blocks direct sun from entering a window at a specific time is known as the:
- Critical shadow angle
- Solar azimuth cutoff angle
- Profile angle (or shadow angle) (Correct answer)
- Declination threshold
Correct answer: Profile angle (or shadow angle)
The profile angle (shadow angle) is the vertical angle of the sun's rays projected onto a plane perpendicular to the window wall, which determines whether a horizontal overhang will cast a shadow on the glazing.
Question 4: Which daylighting strategy is most effective for a school classroom to provide diffuse illumination without direct solar penetration on the learning surface?
- South-facing full-height glazing with no shading
- Bilateral daylighting with north-facing primary windows and south-facing high windows with overhangs (Correct answer)
- East-facing floor-to-ceiling curtain wall
- Roof monitors with south-facing glazing and no reflectors
Correct answer: Bilateral daylighting with north-facing primary windows and south-facing high windows with overhangs
Bilateral daylighting using north windows for steady diffuse light and south high windows with overhangs to admit controlled winter sun provides balanced, glare-free illumination appropriate for classrooms.
Question 5: In IES LM-83-12, the spatial Daylight Autonomy target of sDA300/50% means that:
- 50% of the occupied hours must have illuminance above 300 lux at all floor points
- At least 50% of the regularly occupied floor area must meet or exceed 300 lux for at least 50% of annual occupied hours (Correct answer)
- The average illuminance must be 300 lux for 50% of occupied days
- 300 lux must be achieved with 50% fewer electric luminaires than baseline
Correct answer: At least 50% of the regularly occupied floor area must meet or exceed 300 lux for at least 50% of annual occupied hours
sDA300/50% requires that at least 50% of the regularly occupied floor area achieves a minimum of 300 lux for at least 50% of annual occupied hours, per IES LM-83.
Question 6: When designing toplighting (skylights) for energy efficiency, which skylight-to-roof-area ratio (SRR) range is typically recommended to balance daylight with thermal performance?
- 0–2%
- 3–6%
- 7–15% (Correct answer)
- 20–30%
Correct answer: 7–15%
An SRR of approximately 7–15% is typically recommended as a balance point that provides adequate daylighting while limiting heat gain and loss through the skylight assembly.
Question 7: A design team wants to use daylighting simulation results to demonstrate compliance with ASHRAE 90.1 daylighting controls requirements. Which simulation output is specifically needed?
- Annual Sunlight Exposure (ASE) maps
- Daylight availability in the primary and secondary sidelit and toplit daylighting zones (Correct answer)
- Spatial Daylight Autonomy (sDA) across the full floor plate
- Luminance maps showing window luminance at peak hour
Correct answer: Daylight availability in the primary and secondary sidelit and toplit daylighting zones
ASHRAE 90.1 requires mandatory daylighting controls in primary and secondary sidelit zones and toplit zones based on zone area, so simulations must delineate daylight availability within these defined zones.
CLD Daylighting Design 5
A CLD candidate is asked to evaluate daylighting in an existing building.
Which instrument would directly measure interior illuminance at a workplane?