CLC CLC Photometry & Color Science 1 — Questions and Answers
Question 1: Which photometric quantity describes the total luminous flux emitted by a light source in all directions, measured in lumens?
- Luminous intensity
- Illuminance
- Luminous flux (Correct answer)
- Luminance
Correct answer: Luminous flux
Luminous flux (measured in lumens) represents the total quantity of visible light emitted by a source in all directions.
Question 2: The Color Rendering Index (CRI) measures a light source's ability to reveal colors compared to which reference source?
- A high-pressure sodium lamp
- A natural or reference illuminant (Correct answer)
- A standard fluorescent tube
- A 4000K LED
Correct answer: A natural or reference illuminant
CRI compares how accurately a light source renders object colors relative to a reference illuminant (daylight or incandescent, depending on CCT).
Question 3: A luminaire with an IES Type II photometric distribution is most appropriate for which application?
- Wide parking lots
- Roadway / streetlighting on a two-lane road (Correct answer)
- Narrow hallways
- Stadium floodlighting
Correct answer: Roadway / streetlighting on a two-lane road
IES Type II distribution provides a medium-spread pattern suited for roadway and streetlighting on two-lane roads.
Question 4: Correlated Color Temperature (CCT) is measured in which unit?
- Candela
- Kelvin (Correct answer)
- Lumen
- Foot-lambert
Correct answer: Kelvin
CCT is expressed in Kelvin (K) and describes the color appearance of a light source from warm (2700K) to cool (6500K+).
Question 5: Luminance is defined as luminous intensity per unit of what?
- Solid angle
- Projected area of the source (Correct answer)
- Floor area
- Wattage
Correct answer: Projected area of the source
Luminance (cd/m²) equals luminous intensity divided by the projected area of the emitting surface, describing perceived brightness.
Question 6: Which IES standard publication is the primary reference for photometric testing and measurement of luminaires in the US?
- IES LM-79 (Correct answer)
- ASHRAE 90.1
- NFPA 101
- ANSI C82
Correct answer: IES LM-79
IES LM-79 defines the approved method for total luminous flux, efficacy, and chromaticity measurements of SSL luminaires.
CLC CLC Photometry & Color Science 1
Which photometric quantity describes the total luminous flux emitted by a light source in all directions, measured in lumens?