CLC CLC Photometry & Color Science 2 — Questions and Answers
Question 1: The MacAdam ellipse is used in lighting to define acceptable limits of what characteristic?
- Luminous flux variation over time
- Color consistency (chromaticity variation) between lamps (Correct answer)
- Thermal performance of LEDs
- Light loss factor calculations
Correct answer: Color consistency (chromaticity variation) between lamps
MacAdam ellipses define the chromaticity region within which two light sources appear identical in color to the human eye.
Question 2: Illuminance is measured in foot-candles (fc) in the US customary system; what is the SI equivalent unit?
- Lux (lx) (Correct answer)
- Candela (cd)
- Lumen (lm)
- Nit (nt)
Correct answer: Lux (lx)
Lux is the SI unit of illuminance; 1 foot-candle equals approximately 10.76 lux.
Question 3: Which phenomenon causes colors to appear differently under a light source with a narrow spectral power distribution compared to broadband white light?
- Luminance contrast
- Metamerism (Correct answer)
- Scotopic adaptation
- Stroboscopic effect
Correct answer: Metamerism
Metamerism occurs when two colors appear to match under one illuminant but differ under another due to differences in spectral reflectance.
Question 4: The TM-30 system improves upon CRI by adding which metric to assess the gamut (saturation) of rendered colors?
- Rf (Fidelity Index) only
- Rg (Gamut Index) alongside Rf (Correct answer)
- R9 score only
- CQS value
Correct answer: Rg (Gamut Index) alongside Rf
TM-30 uses both Rf (fidelity) and Rg (gamut index) to give a more complete picture of color rendering quality than CRI alone.
Question 5: In photometry, a candela (cd) measures which quantity?
- Luminous flux in a full sphere
- Luminous intensity in a specific direction (Correct answer)
- Illuminance on a surface
- Surface luminance
Correct answer: Luminous intensity in a specific direction
The candela is the SI unit of luminous intensity, representing the power of light emitted in a specific direction per unit solid angle.
Question 6: An IES photometric data file (.ies) contains luminous intensity values organized by which two angular coordinates?
- Azimuth and altitude
- Vertical (theta) and horizontal (phi) angles (Correct answer)
- Pitch and roll
- Latitude and longitude
Correct answer: Vertical (theta) and horizontal (phi) angles
IES files store candela values at discrete vertical (theta) and horizontal (phi) angle pairs to fully define a luminaire's distribution.
CLC CLC Photometry & Color Science 2
The MacAdam ellipse is used in lighting to define acceptable limits of what characteristic?