Lighting 2 quiz 2

What is the need for color matching

Need a set of functions for standardization that represents the ability of a standard observer to visually match colors

Describe the color matching experiment

Using a set of saturated lights (“primaries”), determine the amount of each primary needed to match a monochromatic light at each wavelength in the visible spectrum

What is the sequence of Color matching functions to chromaticity

Light source SPD x x,y,z Color matching functions (x bar (lambda), y bar (lambda), z bar (lambda) = Tristimulus values (X,Y,Z) → Chromaticity coordinates (x,y)

How do you find X,Y,Z tristimulus values

Integral of light source spectral power distribution times CIE 1931 color matching functions over 380 - 780 nm
Integral [P(lambda)*xbar, ybar, zbar (lambda) d(lambda)]₃₈₀⁷⁸⁰

How do you find x,y chromaticity coordinates from X,Y,Z tristimulus values

x = X / X + Y + Z

y = Y / X + Y + Z

Describe a light source’s “color point”

Any light source SPD can be reduced to a coordinate (point in x,y chromaticity space)

How is the CIE 1931 xy chromaticity diagram boundary formed

Converts every x,y,z color matching function for every SPD wavelength to X,Y,Z coordinates, then convert those to xy coordinates

What is the curved boundary called on the CIE 1931 chromaticity diagram

Spectrum locus

What is the flat boundary at the bottom of the CIE 1931 chromaticity diagram called

Purple line

What are some important points about color matching functions

Not everyone has the same color matching functions as the “standard observer”

No single standard observer can account for individual differences

There is evidence to suggest that using the 2 degree observer causes unnecessary mismatches among observers

The 2 degree field of view size is not representative of vision in building interiors

There are many color matching functions, some of which use a larger field size such as 10 degrees

Members of the IES color committee have developed a new chromaticity system using the 2015 10 degrees standard observer

Why are some of the rgb color matching functions negative in some places?

Since human cones overlap in sensitivity, some pure spectral colors like cyans or greens, cannot be matched by simply mixing red green and blue. Adding a bit of primary light directly to the test color side de-saturates it so the remaining primaries can match the hue. The added primary light to the test sample instead of the mixture is treated as a negative amount of that primary.

What do color matching functions describe

How the human visual system matches colors. They are derived experimentally.

What color matching functions are most common in industry

1931 2 degrees XYZ CMFs

What does the chromaticity coordinate used for

To predict the color appearance of that light

Are the CIE 1931 2 degrees XYZ color matching functions universally applicable?

No, but we use them anyways