CLC Photometry & Color Science Flashcards

The MacAdam ellipse is used in lighting to define acceptable limits of what characteristic?

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.

Illuminance is measured in foot-candles (fc) in the US customary system; what is the SI equivalent unit?

Answer: Lux (lx)

Lux is the SI unit of illuminance; 1 foot-candle equals approximately 10.76 lux.

Which phenomenon causes colors to appear differently under a light source with a narrow spectral power distribution compared to broadband white light?

Answer: Metamerism

Metamerism occurs when two colors appear to match under one illuminant but differ under another due to differences in spectral reflectance.

The TM-30 system improves upon CRI by adding which metric to assess the gamut (saturation) of rendered colors?

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.

In photometry, a candela (cd) measures which quantity?

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.

An IES photometric data file (.ies) contains luminous intensity values organized by which two angular coordinates?

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.