Reflectance and transmittance describe two different paths through a color measurement. Reflectance measures the light returned from a sample. Transmittance measures the light that passes through it. Neither is universally better: the correct mode is the one that represents the product and the decision you need to make.
The core difference
| Mode | What is measured | Typical samples |
|---|---|---|
| Reflectance | Light returned from the illuminated surface under a defined geometry. | Paint, paper, textiles, opaque plastics and coated building products. |
| Transmittance | Light passing through the specimen into the receiving optics. | Clear liquids, films, sheets, glass and transparent plastics. |
A reflectance spectrum and a transmittance spectrum are not interchangeable. Even when both are converted to L*a*b*, they describe different optical events and can respond differently to thickness, scattering, surface finish and backing.
Choose the mode from the product question
01
Define the end use
Decide whether customers judge the surface, the color seen through the material, or both.
02
Classify the sample
Separate opaque, translucent and transparent products before selecting optics or fixtures.
03
Lock the condition
Specify geometry, aperture, path length, backing, orientation and calculation settings.
Translucent samples need an explicit decision
Translucent materials both transmit and scatter light. A backed reflectance method can be valid when the product is always viewed against a defined substrate, but the result describes that sample-and-backing combination. A transmission method is more suitable when the requirement concerns the light passing through the material. Haze is a separate scattering property and should not be inferred from a color value alone.
Do not compare unlike modes
A supplier’s transmission result should not be accepted against a reflectance target without a documented correlation. Match the optical mode and sample presentation at every site.
Record enough information to reproduce the result
For reflectance, record geometry, SCI or SCE where relevant, aperture, backing and surface orientation. For transmission, record total or regular transmission, specimen thickness or liquid path length, cell type, blank or reference procedure and placement. Continue with spectral reflectance, plastic color measurement and integrating spheres.
Last reviewed 21/09/2026 · Level: Fundamental
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