Professional Detailing2 min read

Weathering Irradiance and Radiant Dose: Keep Rate and Total Separate

Irradiance describes an exposure rate, while radiant dose describes accumulated energy. A coating test report needs the appropriate quantities and units; replacing one with the other can obscure how the exposure was delivered.

Updated · NANOLAB Knowledge

The key distinction

Q-Lab distinguishes these measurements in its weathering guidance. For a coating buyer, the important step is to keep the exposure history attached to the result. A total alone does not describe the spectrum, temperature or moisture conditions, and a rate alone does not describe how long the sample experienced it.

Practical checks

  1. Ask the laboratory to identify the controlled irradiance and the accumulated exposure where relevant.
  2. Retain the wavelength basis and units in the comparison table.
  3. Review the complete exposure cycle before comparing durability observations.

Example

Illustrative example: one report lists a rate and another lists a total dose. A buyer cannot rank the samples by choosing the larger printed number. The reports first need to be interpreted in their own units and matched to the actual exposure conditions and evaluation endpoint.

Scope and limits

Do not convert an energy total directly into years of outdoor coating life. This article explains report terminology, not a lifetime prediction method. Product claims require evidence that connects the relevant test, failure mechanism and intended service conditions.

Related guidance

Technical references: Q-Lab: Radiant dosage in exposure tests. These sources describe their stated methods or products; they do not certify NANOLAB products or establish compatibility with an unlisted surface.

Ask NANOLAB about the exact product and intended use. Use the current product documentation for formulation-specific instructions.