Short answer
Decide first whether the sample is to be judged by reflected or by transmitted light, then control where the rest of the light goes. In reflection, a translucent sample loses light through its back and sideways beyond the measuring port, so the backing, the thickness and the port size all become part of the result. In transmission, a clear sample can sit anywhere in the beam, but a hazy one must be pressed against the sphere so that scattered light is collected. Without those details the numbers cannot be repeated.
An opaque sample returns light from the spot that was lit. A translucent one lets light travel inside it. Some passes through and is reflected, absorbed or lost by whatever lies behind. Some spreads sideways and emerges outside the area the instrument views, or is absorbed by the edge of the port. The second loss has been studied in the graphic arts under the names lateral diffusion, translucent blurring and edge loss, and it depends on the relative sizes of the illuminated and viewed areas, so two instruments with different apertures disagree on the same translucent sample even when both are in calibration. Both losses vary with wavelength, since light that is weakly absorbed travels furthest, so they alter hue as well as lightness.
HunterLab's method sheet for flat translucent solids sets out the usual remedies. Give the sample a constant background: a white backing tile, or enough folded or stacked layers that adding another changes nothing. Use the largest port the sample will cover while viewing a smaller area inside it, so that light scattered sideways within the sample is still returned and measured. Keep room light off the sample, to which a translucent specimen is sensitive. Rotate it between readings and average, because sheets and plaques are often directional. And if the material is a white that may contain brightener, control the ultraviolet. Whichever backing is chosen becomes part of the specification: a reading over white and a reading over black are both valid, and they are different colours.
For liquids, films and glazing the colour that matters is usually the transmitted one. A perfectly clear specimen sends light straight on, and ASTM E1348 treats it as measurable wherever it sits in the beam. A hazy or translucent specimen scatters part of the light into a wide cone; only if it is placed flush against the entrance port of an integrating sphere is that scattered light collected, and the same standard requires that placement. ASTM D1003 uses the distinction as a measurement in itself: haze is the share of transmitted light scattered at wide angles, obtained by hazemeter or by spectrophotometer, with the caution that the two procedures give slightly different values and that material above 30% haze counts as diffusing and belongs to a different practice.
A colour value for a non-opaque sample is incomplete without its presentation. For reflection: backing (and its own colour if it is not a calibrated tile), thickness or number of layers, port and viewed-area sizes, specular mode, and whether readings were rotated and averaged. For transmission: path length or thickness, whether transmission was regular or total, position relative to the sphere, and the reference used for 100%, air or a cell filled with clear solvent. For both, the instrument geometry and the usual illuminant and observer. Where a product is seen both ways, such as a tinted bottle or a lampshade, the two measurements describe different things and neither replaces the other.
| Sample | Mode | Presentation | Record with the result |
|---|---|---|---|
| Clear film, glass or liquid | Regular or total transmission | Anywhere in the beam; liquids in a cell of fixed path length | Thickness or path length; what was used as 100% |
| Hazy film or sheet | Total transmission and haze | Flush against the sphere's entrance port | Thickness; hazemeter or spectrophotometer procedure |
| Translucent plaque, paper or fabric seen by reflected light | Reflection | Over a stated backing or stacked to opacity; port larger than viewed area; rotated and averaged | Backing or number of layers; port and view sizes; specular mode |
| Product seen both ways (tinted bottle, shade, diffuser) | Both, reported separately | As above for each | Which measurement the tolerance applies to |
Why: The hand-held instrument illuminates and views nearly the same small area, so more of the light that spreads sideways inside the plaque escapes it.
Fix: Compare only readings made with the same aperture arrangement, or use the instrument with the larger port and smaller view for both.
Why: The clamp's face is acting as the backing, and the two clamps differ in colour.
Fix: Back the sample with a dedicated white tile or stack to opacity, and name the backing in the method.
Why: On one the film sat away from the port, so part of the scattered light missed the sphere.
Fix: Place the specimen flush against the entrance port every time.
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.
FactModerate evidence
When a translucent sample is measured in reflection, light that diffuses sideways inside it beyond the viewed area is lost to the measurement, an error known as lateral diffusion, translucent blurring or edge loss, whose size depends on the instrument's illumination and viewing apertures.
Caveat: From a conference paper's abstract and a maker's method sheet; no figure for the size of the error is quoted because it depends on the sample and the instrument.
Source: Using Translucency Standards to Evaluate Color Instrument Lateral Diffusion Errors; Measurement Method MM 5071.00: Measuring Flat, Translucent Solids
ConventionModerate evidence
A maker's method for flat translucent solids on a sphere instrument recommends a constant backing or stacking to opacity, a port larger than the area viewed, and averaging readings taken with the sample rotated by 90°, and notes that such samples are sensitive to ambient light.
Caveat: One manufacturer's recommended practice for its own instrument.
Source: Measurement Method MM 5071.00: Measuring Flat, Translucent Solids
StandardStrong evidence
ASTM E1348 treats fully transparent specimens as measurable in transmission regardless of their position relative to the sphere's transmission port, but requires translucent or hazy specimens to be placed flush against that port, and is not recommended for fluorescent specimens.
StandardStrong evidence
ASTM D1003 provides a hazemeter procedure and a spectrophotometer procedure for haze and luminous transmittance of essentially transparent plastics, notes that hazemeter values are normally slightly higher and less variable, and treats material with haze above 30% as diffusing and outside the method.
Source: ASTM D1003-21 Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
Colourwise interpretationModerate evidence
For a non-opaque sample the backing, thickness and aperture are part of the measured colour, so a value reported without them cannot be reproduced.
Based on: Follows from the two loss mechanisms described in the cited method sheet and conference paper: both depend on what is behind the sample and on the size of the viewed and illuminated areas.
Reviewed 6 October 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.