Transmittance vs reflectance measurement
Whether colour is measured in reflected or transmitted light depends on the material. We explain when to choose transmittance and when reflectance.
Two paths of light
Colour can be measured in two ways, depending on how light interacts with the material:
- Reflectance — measures light reflected off the surface. This is the method for opaque materials: textiles, plastics, paints, coatings, paper, powders.
- Transmittance — measures light passing through the sample. This is the method for transparent and translucent materials: liquids, films, glass, filters.
How to choose the method
The nature of the sample decides:
- Opaque material → reflectance. A standard spectrophotometer or colorimeter.
- Clear liquid (solvents, oils, beverages, pharmaceuticals) → transmittance. A dedicated transmission spectrophotometer such as the TS4020 reports colour and industrial scales (APHA, Gardner, Saybolt).
- Hazy or suspended liquid (pulpy juices, milk) → reflectance is often better, because light is strongly scattered.
- Films, glass, packaging → transmittance and haze measurement with a haze meter per ASTM D1003.
Some benchtop instruments, such as the YS6060 and TS8560, combine both measurements — reflectance and transmittance — in a single unit.
Frequently asked questions
When should I measure in transmittance vs reflectance?
Opaque materials (textiles, plastics, paints) are measured in reflectance. Transparent materials and clear liquids — in transmittance. Hazy materials can be an exception: with strong light scattering, reflectance is sometimes better.
Can one instrument measure both reflectance and transmittance?
Yes — some benchtop spectrophotometers (e.g. YS6060, TS8560) have both geometries and can measure opaque samples as well as transparent ones and liquids.
What is the difference between transmittance and haze?
Transmittance is the total amount of light passing through the material, while haze is the fraction of light scattered at wide angles, responsible for a "milky" appearance. Both are measured with a haze meter per ASTM D1003.