Spectrum and Color Analysis

This chapter covers the 6 result pages in the spectrum/color group:

• Reflection Spectrum
• Transmission Spectrum
• Absorption Spectrum
• Reflection Color
• Transmission Color
• Absorption Color

These pages extend the basic optical response into two practical views:

1. how the energy is distributed across wavelength under the current incident spectrum
2. what color that distribution becomes after it is converted into a visible-color result

Analysis Entry

Focus

This chapter covers three points:

1. what the ...Spectrum and ...Color pages provide
2. the availability conditions created by incident-spectrum and color-calculation settings
3. how the page switches between single-run, one-parameter sweep, and multi-parameter sweep presentations

Example Setup: D65 Visible-Color Baseline

The single-run screenshots in this chapter use a reproducible “default ITO coating under D65” case. The purpose is not to maximize saturation; it is to produce a stable baseline that shows the spectrum page, chromaticity chart, and color card with one consistent setup.

This example uses:

1. The unchanged default Structure: Air-in -> ITO (40 nm) -> Substrate (1 um, Incoherent) -> Air-out.
2. Incident Spectrum enabled in Optics, keeping the default source Illuminant D65.
3. Visible Color enabled.
4. The Set spectrum 360–780 nm, step 1 preset, so the wavelength settings satisfy the hard color-calculation rule.
5. The top-toolbar Run button to generate the single-run color result.

Availability conditions

The first rule is simple: these pages appear only when the current run actually produced the required data.

The current implementation uses these visibility rules:

In practice:

• If the wavelength mode is Single or Average, Reflection Spectrum / Transmission Spectrum / Absorption Spectrum will not be available.
• If visible-color calculation is not enabled, the color pages stay unavailable because no color object is produced.

The hard prerequisites for color calculation are still:

1. Incident Spectrum must be enabled.
2. Enable Color Calculation must be enabled.
3. the wavelength range must be 360 nm -> 780 nm.
4. the wavelength step must be <= 1 nm.

If any one of these fails, the color result is not generated.

Spectrum pages

Reflection Spectrum, Transmission Spectrum, and Absorption Spectrum are not just renamed R / T / A plots.

They show spectral output under the current incident-spectrum setup. For example, Reflection Spectrum currently plots:

• Incident Spectrum: the source spectrum itself
• Spectral Intensity (a.u.): the reflected spectral intensity

So the page answers questions like:

• under this light source, which wavelengths dominate the reflected output?
• if the source changes from Illuminant D65 to a custom spectrum file, how should the visible color shift?

Table usage:

1. read the gray Incident Spectrum first so you know where the source injects energy
2. read the colored target curve second so you see how reflection/transmission/absorption redistributes that energy
3. connect that distribution to the matching color page to explain the final hue or tint

These pages are especially useful for light-source sensitivity checks. Two designs can look similar in raw R behavior while producing noticeably different visible-color outputs under different illuminants.

Color pages

Reflection Color, Transmission Color, and Absorption Color all use the same UI pattern, but the actual content changes with run mode.

The current behavior is:

That means:

1. the color pages do not default to numeric cards; they default to the chromaticity chart
2. in a single run, switching to table view shows a color card
3. in a sweep, switching to table view shows the sweep color table
4. once the sweep has 2 or more parameters, the chart/table toggle disappears and the page stays in table mode

So if the view toggle is missing, check the sweep dimensionality first. That is the intended behavior.

Chromaticity diagram

The default view of each color page is the CIE 1931 Chromaticity Diagram.

This chart is best for questions like:

• where the current result sits inside color space
• whether a parameter sweep moves the result along a smooth path or jumps in a narrow region

The current chart layout is:

1. the central plot area shows the xy point
2. the right-side panel controls reference overlays and chart presentation
3. the lower info block reports how many data points are currently plotted

The right-side controls currently include:

• sRGB
• NTSC
• DCI-P3
• BT.2020
• Show Color Background
• Planckian Locus
• Wavelength Labels

When more than one point exists, the panel also adds:

• Connect Data Points

That switch matters because it turns a set of isolated sweep points into a visible path, which makes directional color drift much easier to interpret.

Do not stop at “is the point inside a triangle?” Also check:

1. how far the point sits from neutral regions
2. whether multiple points move along a consistent path
3. whether that motion matches the parameter trend you expect

Color card

In a single run, switching a color page to table view shows the color card, not a generic grid.

The card splits the result into two groups:

Use:

1. use XYZ / xy / xyY for physics-oriented or colorimetry-oriented analysis
2. use sRGB (8-bit) and Hex when you need a display-ready color value
3. use the copy buttons for one-off transfer into another tool
4. use Export CSV if you want the entire record archived

This view is meant for one resolved color result. Once you are comparing multiple parameter combinations, the sweep table is usually the better working surface.

Sweep color table

When a color result is generated in sweep mode, the page can switch into SpectrumColorSweepDataTable.

If the sweep has 2 or more parameters, this table is forced and the chromaticity chart is no longer available from that page.

The sweep table below uses the same structure and the same color-ready optics setup, then adds the default two-parameter sweep:

1. Open the Sweep page.
2. Keep optics/incidentAngle enabled and narrow it to 0 -> 60 with step 30.
3. Keep optics/pRatio enabled with the default 0 -> 1 range and step 0.5.
4. Click Run Sweep, which produces 3 × 3 = 9 color combinations.

Reading checklist:

1. read the left parameter columns to identify the active combination
2. use the Color swatch column for fast visual grouping
3. open only the numeric columns you need

The table currently contains three kinds of columns:

The checkboxes in the toolbar control which color-value columns are visible. A practical workflow is:

1. keep only xy or Hex visible to shortlist candidates quickly
2. then reopen XYZ / xyY / sRGB for detailed comparison
3. export the final table with Export CSV

Use this page to judge:

• which parameter combination is closest to the target color?
• which candidate preserves optical performance while minimizing color shift?
• is color drift driven more by angle or by pRatio?

Effect of incident spectrum

The key distinction is:

The basic Reflectance / Transmittance / Absorptance pages describe the stack response itself. The ...Spectrum and ...Color pages describe the combination of:

• the stack response
• the selected incident spectrum

Changing any of the following:

• the incident-spectrum source type
• the imported source-spectrum file
• the relative energy weighting inside the visible band

can directly change:

1. the shape of the spectrum curve
2. the values in XYZ / xy / sRGB / Hex
3. the point location in the chromaticity chart

But it does not directly change the underlying raw R / T / A response of the optical stack.

Workflow:

1. validate the stack itself on the basic result pages first
2. then validate how that stack looks under the intended light source on the spectrum/color pages

Common errors and checks

Missing ...Spectrum pages

Check these first:

1. whether wavelength mode is Sweep rather than Single / Average
2. whether Incident Spectrum is enabled
3. whether the run actually produced the corresponding spectrum array

Missing ...Color pages

Check these first:

1. whether Enable Color Calculation is enabled
2. whether the wavelength range is exactly 360 -> 780 nm
3. whether the step is <= 1 nm
4. whether you re-ran the calculation after changing optics settings

Missing color-page toggle

This usually means the current sweep has >= 2 parameters, so the page is intentionally forced into table mode.

Single-point chromaticity plot

That usually just means you are looking at a single calculation result, or only one valid color point is currently available.

Unexpected reported color

Do not blame the material file first. Check these in order:

1. whether the active incident-spectrum source is correct
2. whether visible-color calculation ran in the proper 360-780 nm range
3. whether you are reading reflection color, transmission color, or absorption color

Next step

If the current task is to use spectral and color outputs inside sweep-driven application analysis, continue with RTA and Layer Absorption Analysis. If the current task moves to polarization sensitivity and angle selection, continue with Ellipsometry Analysis.