CLD Lighting Design Principles & Techniques 3 — Questions and Answers
Question 1: What distinguishes 'ambient' lighting from 'task' lighting in a layered lighting design?
- Ambient lighting uses warmer color temperatures than task lighting
- Ambient provides general background illumination while task lighting delivers focused light for specific activities (Correct answer)
- Task lighting is always ceiling-mounted while ambient lighting is portable
- Ambient lighting requires dimming controls but task lighting does not
Correct answer: Ambient provides general background illumination while task lighting delivers focused light for specific activities
Ambient lighting establishes overall baseline illumination for a space, while task lighting supplements it with higher, directed light for work activities like reading or cooking.
Question 2: What is the recommended maintained illuminance level for a general office work environment per the IES Lighting Handbook?
- 50 lux (5 fc)
- 300–500 lux (30–50 fc) (Correct answer)
- 1000 lux (100 fc)
- 150 lux (15 fc)
Correct answer: 300–500 lux (30–50 fc)
The IES recommends 300–500 lux (approximately 30–50 footcandles) as the maintained illuminance target for general office tasks.
Question 3: A designer uses a 'scallop' effect on a wall. How is this typically achieved?
- By using linear fluorescent strips at the wall base
- By spacing recessed downlights too far from the wall, creating overlapping semi-circular patterns (Correct answer)
- By mounting fixtures at ceiling height aimed toward the floor
- By using prismatic diffusers on surface-mounted fixtures
Correct answer: By spacing recessed downlights too far from the wall, creating overlapping semi-circular patterns
Scalloping occurs when recessed downlights are positioned far enough from a wall that their circular beam patterns land as overlapping scallop shapes rather than an even wash.
Question 4: What is the role of the 'adaptation luminance' concept when designing for transitions between interior and exterior spaces?
- It determines the color temperature shift needed at entry points
- It accounts for the eye's adjustment time to different brightness levels, preventing discomfort or hazard (Correct answer)
- It specifies the minimum lumen output for lobby fixtures
- It defines the reflectance value required for threshold surfaces
Correct answer: It accounts for the eye's adjustment time to different brightness levels, preventing discomfort or hazard
Adaptation luminance guides how transition zones should be lit to allow the eye to adjust gradually between very bright and very dim environments, reducing safety hazards.
Question 5: Which metric is used to evaluate a light source's ability to render human skin tones accurately?
- CRI R9 value (Correct answer)
- Correlated Color Temperature (CCT)
- Luminous efficacy
- Unified Glare Rating (UGR)
Correct answer: CRI R9 value
The R9 value within the CRI system specifically measures how accurately a light source renders saturated red, making it critical for evaluating skin tone reproduction.
Question 6: In theatrical lighting, what is the function of a 'gobo'?
- A barn door attachment to control spill light
- A metal or glass template inserted into an ellipsoidal fixture to project a pattern or shape (Correct answer)
- A diffusion filter that softens hard shadows
- A color correction gel for tungsten sources
Correct answer: A metal or glass template inserted into an ellipsoidal fixture to project a pattern or shape
A gobo is a thin metal or glass disc with a cut-out pattern placed in the focal plane of an ellipsoidal (leko) fixture to project shapes, textures, or images onto surfaces.
Question 7: What is 'luminance contrast' and why does it matter in a visual display terminal (VDT) work environment?
- The difference in CCT between ceiling and task lighting; affects alertness
- The ratio of luminance between the screen and surrounding surfaces; high contrast causes visual fatigue (Correct answer)
- The variation in lumen output across a luminaire's surface; affects uniformity
- The difference between direct and reflected glare; affects fixture spacing
Correct answer: The ratio of luminance between the screen and surrounding surfaces; high contrast causes visual fatigue
In VDT environments, excessive luminance contrast between bright screens and dark surroundings forces the eye to constantly readapt, leading to eyestrain and fatigue.
CLD Lighting Design Principles & Techniques 3
What distinguishes 'ambient' lighting from 'task' lighting in a layered lighting design?