CLD Photometry & Light Measurement 1 — Questions and Answers
Question 1: What unit is used to measure luminous flux?
- Lumen (Correct answer)
- Candela
- Lux
- Watt
Correct answer: Lumen
Luminous flux is measured in lumens (lm), representing the total quantity of visible light emitted by a source.
Question 2: Which unit measures illuminance, the amount of light falling on a surface?
- Candela per square meter
- Lux (Correct answer)
- Lumen
- Watt per square meter
Correct answer: Lux
Illuminance is measured in lux (lx) in SI units, representing lumens per square meter of surface area.
Question 3: A goniophotometer is primarily used to measure:
- Color rendering index of a lamp
- Luminous intensity distribution of a luminaire (Correct answer)
- Total luminous flux using an integrating sphere
- Correlated color temperature
Correct answer: Luminous intensity distribution of a luminaire
A goniophotometer measures the luminous intensity distribution of a luminaire at various angles, producing photometric data used in lighting calculations.
Question 4: According to the inverse square law, if the distance from a point source doubles, the illuminance on a surface:
- Doubles
- Remains the same
- Decreases by half
- Decreases to one-quarter (Correct answer)
Correct answer: Decreases to one-quarter
The inverse square law states illuminance is inversely proportional to the square of the distance, so doubling the distance reduces illuminance to 1/4.
Question 5: Luminous intensity is measured in which unit?
- Lumen
- Lux
- Candela (Correct answer)
- Nit
Correct answer: Candela
Luminous intensity, which describes the power of a light source in a particular direction, is measured in candelas (cd), the SI base unit for photometry.
Question 6: What is the SI unit for luminance?
- Lux
- Candela per square meter (cd/m²) (Correct answer)
- Lumen per steradian
- Footlambert
Correct answer: Candela per square meter (cd/m²)
Luminance, describing the perceived brightness of a surface as seen by the eye, is measured in candela per square meter (cd/m²), also called nits.
Question 7: The Color Rendering Index (CRI) is measured on a scale from 0 to:
- 50
- 100 (Correct answer)
- 200
- 1000
Correct answer: 100
CRI is measured on a scale from 0 to 100, where 100 represents perfect color rendering equal to a reference illuminant such as daylight.
CLD Photometry & Light Measurement 1
What unit is used to measure luminous flux?