Measurement geometry — 45°/0° vs d/8°
Geometry determines how an instrument "sees" a sample. We explain the difference between directional 45°/0° and sphere d/8° geometry, plus the SCI and SCE modes.
Why geometry matters
A colour reading depends not only on the sample itself but also on the angle at which it is illuminated and viewed. That is why standards define measurement geometries. The two most important are directional 45°/0° and sphere d/8°.
45°/0° geometry
The sample is illuminated at 45° and light is collected perpendicularly (0°) — or the reverse. This geometry removes the influence of gloss and closely reproduces how the human eye assesses the colour of a matte or textured surface. It suits control of textiles, plastics, ceramics, printing and retro-reflective materials. One such instrument is the TS-26C spectrophotometer.
Sphere d/8° geometry
The sample is illuminated by the diffuse light of an integrating sphere and viewed at 8°. The d/8° geometry makes the reading independent of gloss and texture, so it is recommended for glossy surfaces, recipe control and whenever samples with different finishes must be compared.
SCI and SCE modes
Sphere geometry offers two modes:
- SCI (Specular Component Included) — includes gloss; it assesses the “pure” colour of the material regardless of surface state. Used in recipe control.
- SCE (Specular Component Excluded) — excludes gloss; the result better matches the visual impression of the finished product.
The best spectrophotometers measure both modes simultaneously. It is worth tying the choice of geometry to the material and standard — we are happy to help you decide.
Frequently asked questions
Which geometry should I choose — 45°/0° or d/8°?
The 45°/0° geometry reproduces visual assessment and suits matte and textured surfaces. The d/8° sphere geometry makes the reading independent of gloss and is recommended for glossy surfaces and recipe control.
What is the difference between SCI and SCE?
SCI includes the specular component (gloss) and assesses the material's colour regardless of finish — the mode for recipes. SCE excludes gloss, so the result better matches what the eye sees on the finished product.
Can results from different geometries be compared?
Not directly. Instruments with different geometries return different values for the same sample, so the standard and the sample should always be measured with the same geometry and in the same mode (SCI or SCE).