Short answer
SCI (specular component included) measures all the light a sample reflects, including the mirror-like gloss reflection; SCE (specular component excluded) traps the gloss and measures only the diffuse light. SCE matches how a surface looks, so a glossy and a matt sample of the same paint read differently. SCI describes the colourant regardless of surface finish, so they read nearly the same. Choose SCE for appearance checks and SCI for formulation.
Light reflected by a surface has two parts. Specular reflection leaves at the mirror angle and carries the colour of the light, not the material: it is a few per cent at every wavelength for most paints and plastics. Diffuse reflection has entered the material, been partly absorbed by colourant, and scattered back out in all directions; this carries the colour. On a glossy surface the specular part is concentrated in one direction and the diffuse part looks deep and saturated from elsewhere. On a matt or sanded surface the same specular light is spread in all directions and mixes with the diffuse colour, which is why sanding a glossy blue part makes it look paler and duller though the pigment has not changed.
In a d/8° sphere instrument the detector looks at the sample 8° off-perpendicular. The mirror reflection of the sphere wall towards the detector comes from a small area at the opposite 8° position. If that area is an open port — a light trap — there is no light there to reflect, so the specular component is missing from the reading: SCE. If the port is closed with a white cap matching the sphere, the specular reflection is present: SCI. Many instruments measure both at once. Directional 45°/0° instruments are inherently SCE-like because the gloss reflection is aimed away from the detector.
SCI's value is that total reflectance — specular plus diffuse — is nearly the same for a given colourant whatever its surface finish. A formulator matching a paint colour does not want a matt and a gloss version to need different recipes, so formulation and colourant-strength work use SCI. SCE's value is that it tracks appearance: if a production part has come out slightly less glossy, SCE reports it as lighter and duller, which is what an inspector would see. Production pass/fail against a visual standard therefore often uses SCE. Using both reveals whether a difference comes from colourant (both change) or surface (only SCE changes).
The split is cleanest for smooth, high-gloss surfaces. For semi-gloss and textured surfaces the specular reflection spreads wider than the trap, so SCE excludes only part of it and results depend on the port size of the particular instrument — a source of disagreement between models. Metallic and pearlescent finishes are a different problem: their colour changes with angle by design, and neither SCI nor SCE from one geometry describes them; multi-angle instruments are used instead. Gloss itself is measured separately with a glossmeter at standard angles.
Why: It is less glossy; SCI ignores the change in surface reflection.
Fix: Check appearance in SCE (or 45°/0°) and gloss with a glossmeter.
Why: SCE reports the lighter look of the matt surface as a colour difference.
Fix: Use SCI for colourant consistency across sheens; keep SCE tolerances per sheen.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
In SCE mode a light trap excludes the specular reflection and only diffuse reflectance is measured; in SCI mode the trap is replaced with a white plug so specular reflectance is included.
Source: Precise Color Communication
FactStrong evidence
SCE correlates with how an observer sees an object's colour, while SCI measures total appearance largely independent of surface condition; SCE suits visual-match verification on production lines and SCI suits colour formulation.
Source: Precise Color Communication
FactStrong evidence
The total amount of reflected light (specular plus diffuse) stays about the same when a glossy surface of a given material is roughened, even though it looks lighter and duller.
Source: Precise Color Communication
Colourwise interpretationModerate evidence
Measuring in both SCI and SCE and comparing the change is a practical way to tell a colourant difference from a gloss difference.
Based on: Follows from SCI being largely insensitive to surface finish while SCE is sensitive to it, as described by the instrument maker.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.