CLD Lighting Fundamentals 2 — Questions and Answers
Question 1: Which photometric quantity describes the total light output of a source in all directions?
- Illuminance
- Luminous flux (Correct answer)
- Luminance
- Luminous intensity
Correct answer: Luminous flux
Luminous flux, measured in lumens (lm), represents the total quantity of visible light emitted by a source in all directions.
Question 2: A light source has a color temperature of 2700K. How would this light typically be described?
- Cool white
- Neutral white
- Warm white (Correct answer)
- Daylight
Correct answer: Warm white
2700K falls in the warm white range, producing a yellowish-amber tone similar to incandescent lamps.
Question 3: What is the inverse square law in lighting?
- Illuminance doubles as distance doubles
- Illuminance is proportional to the square of the distance
- Illuminance decreases as the square of the distance increases (Correct answer)
- Illuminance increases as the square of the distance increases
Correct answer: Illuminance decreases as the square of the distance increases
The inverse square law states that illuminance (E) decreases proportionally to the square of the distance (d) from a point source: E = I/d².
Question 4: What term describes the ratio of luminous flux reflected by a surface to the flux incident upon it?
- Transmittance
- Reflectance (Correct answer)
- Absorptance
- Efficacy
Correct answer: Reflectance
Reflectance is the ratio of reflected luminous flux to incident luminous flux, expressed as a decimal or percentage.
Question 5: Which of the following best defines 'luminous efficacy' of a light source?
- Lumens per watt (lm/W) (Correct answer)
- Candelas per square meter (cd/m²)
- Lumens per square meter (lm/m²)
- Watts per steradian (W/sr)
Correct answer: Lumens per watt (lm/W)
Luminous efficacy is the ratio of luminous flux output to electrical power consumed, expressed in lumens per watt (lm/W).
Question 6: What does a Lambertian surface do with incident light?
- Reflects all light at the specular angle
- Emits or reflects light with equal luminance in all directions (Correct answer)
- Absorbs all incident light uniformly
- Transmits light without scattering
Correct answer: Emits or reflects light with equal luminance in all directions
A Lambertian (perfectly diffuse) surface has constant luminance regardless of the viewing angle, scattering light equally in all directions.
Question 7: In photometry, what is a steradian (sr)?
- A unit of luminous flux
- A unit of solid angle (Correct answer)
- A unit of illuminance
- A unit of color temperature
Correct answer: A unit of solid angle
A steradian is the SI unit of solid angle, and a full sphere subtends 4π steradians around a point.
CLD Lighting Fundamentals 2
Which photometric quantity describes the total light output of a source in all directions?