IEC 60721-2-4:2018

Overview

IEC 60721-2-4:2018 - Classification of environmental conditions, Part 2-4 - defines types and severities of solar radiation and temperature that products can be exposed to in nature. The standard is intended as background material for selecting appropriate solar-radiation severities for product design, testing, storage and transport. It covers global irradiation and peak irradiance levels for all geographic areas below 5 000 m altitude and includes updated figures and global irradiation maps in this edition.

Key topics

• Solar radiation physics: spectrum of solar energy reaching the Earth (mostly 0.3 µm–4 µm), concept of global radiation (direct + diffuse), and the solar constant (~1 367 W/m²).
• Levels of global radiation: recommended peak global irradiance values for cloudless noontime conditions (typical peak ~1 120 W/m²; short-term reflections can reach ~1 300 W/m²).
• Mean and extreme values: monthly and annual global irradiation distributions, and world maps/annex showing relative irradiation by region.
• Nighttime atmospheric radiation: minimum sky radiation values relevant for “under temperature” calculations.
• Heating and photochemical effects: guidance on how irradiance contributes to surface heating and UV-driven degradation of organic materials (bleaching, loss of elasticity).
• Artificial air temperature concept: relationship between air temperature, irradiance (E), surface absorptance (αs) and heat transfer coefficient (hy). Example parameters given (αs ≈ 0.7, hy ≈ 20 W/(m²·°C), E = 900 W/m²) illustrating an over-temperature of ≈30 °C.
• Usage notes: excludes altitudes above 5 000 m and directs users to IEC 60721-1 for applying classification severities.

Applications

IEC 60721-2-4 is practical for:

• Product design and materials selection: quantify thermal loading and UV exposure for plastics, rubbers, coatings, optical glass, and color-coded components.
• Environmental testing and qualification: set test severities for lab simulations of solar heating and photochemical aging.
• Transport, storage and installation planning: determine worst-case exposure during logistics and outdoor deployment.
• Manufacturers, test labs and procurement teams: use the classification to specify requirements, evaluate conformity and compare products across geographic climates.
• Standards committees and researchers: reference global irradiation maps and quantitative irradiance values.

Related standards

• IEC 60721-1 - referenced for applying classification severities and integrating solar-radiation severities into broader environmental condition classifications.
• Other parts of the IEC 60721 series cover additional environmental condition types (see IEC catalogue for the series).

Keywords: IEC 60721-2-4, solar radiation classification, global irradiation, irradiance, environmental conditions, product testing, photochemical degradation, thermal loading, climatic classification.