ISO 20589:2025

This document specifies a procedure for determining the emissivity at room temperature of the surfaces of glass and coated glass.

The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing according to ISO 9050[5], ISO 10291[6], ISO 10292[7], and ISO 10293[8].

The procedure, being based on spectrophotometric specular reflectance measurements at near normal incidence on materials that are non-transparent in the infrared region, is not applicable to glazing components with at least one of the following characteristics:

a)       with rough or structured surfaces where the incident radiation is diffusely reflected;

b)       with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to reach the detector while using specular reflectance accessories;

c)        infrared transparent.

However, it can be applied with caution to any glazing component provided its surfaces are flat and non-diffusing (see non-diffusing glazing component) and it is non-transparent in the infrared region (see glazing component non-transparent in the infrared region).

Although transmittance measurements are included in this document, they are only necessary to check if the specimen is non-transparent in the infrared region in the context of this document (see glazing component non-transparent in the infrared region). If the specimen is transparent in the infrared region, this document is not applicable.