Color Evaluation

Color Evaluation turns a coating’s spectrum into a perceived color. It takes the reflectance or transmittance across the visible range, weights it by a standard observer and illuminant, and reports where the result sits on the CIE chromaticity diagram along with a color swatch and a full set of color-space values. Use it to predict the visible appearance of a coating: the tint of an antireflection film, the hue of a decorative mirror, or how a filter shifts color with viewing angle.

The spectrum is sampled across 380–780 nm and fed through the standard colorimetric integral, so the color matches the curves shown in Optical Evaluation.

Settings

Characteristic: compute the color of reflected (R) or transmitted (T) light.

Polarization: average, s, or p. Average is the usual choice for unpolarized illumination.

AOI: the viewing angle in degrees. Sweep this to see how an iridescent coating shifts color with incidence.

Observer: the CIE color-matching functions: the 1931 2° observer for small fields or the 1964 10° observer for larger fields.

Illuminant: the light source the color is computed under: daylight (D65, D50), incandescent (A), and equal-energy (E).

Step: the wavelength sampling interval in nm for the color integral. A finer step improves accuracy on coatings with sharp spectral features.

Exposure: the brightness of the color swatch only. By default the swatch is scaled against a perfect white reflector, so a very dim reflection (such as the residual color of a strong antireflection coating) renders almost black even when its hue is highly saturated. Raise the exposure (×10 up to ×1000) or choose Fit hue to rescale the swatch and reveal the hue at full brightness. The numeric readout does not change; only the swatch is re-exposed. This mirrors what the eye sees when the coating reflects a bright source instead of a dim scene.

The evaluation surface (front, back, or total) is set in the Design Editor and shown as a badge on the window.

How to read it

The chromaticity diagram shows the spectral locus (the horseshoe of pure colors, closed by the purple line) with wavelength marks every 20 nm from 460 to 620 nm, the white point of the chosen illuminant, and a marker for your coating. A marker near the white point means a near-neutral, colorless coating; a marker pulled toward an edge of the locus means a strong, saturated tint. Two swatches in the corner of the diagram show the coating’s color as an approximate on-screen color, with its Y, next to the reference white of the illuminant.

Because the swatch is referenced to a perfect white reflector, a dim reflection looks dark or black even when the chromaticity marker sits far out toward the locus: the color is genuinely there, but there is little reflected light to carry it. Use the Exposure setting to bring that hue up to a visible brightness without changing the reported values.

The numeric panel reports tristimulus X, Y, Z; xy, u′v′ and CIE 1960 uv chromaticity; CIE L*a*b* and L*u*v* with their chroma and hue angles; Hunter Lab; the dominant wavelength, or for a purple, which has none, the complementary wavelength, each with its purity; and correlated color temperature (CCT) with its offset from the Planckian locus (Duv). CCT reads as a dash for a color too far from the Planckian locus to have one.

References

• CIE 15:2004, Colorimetry, 3rd ed.
• H. A. Macleod, Thin-Film Optical Filters, 5th ed., §12.2 (Eqs. 12.1–12.5).