ASTM G173 is the standard reference for solar spectral irradiance data, providing a consistent basis for direct normal and hemispherical irradiance on a 37° tilted surface. It matters because it supports apples-to-apples comparison in solar-related testing, modeling, and product evaluation. By using a recognized ASTM standard, users can work from a common spectral reference rather than relying on inconsistent assumptions or ad hoc datasets, which helps improve technical consistency and communication.

What is ASTM G173?

ASTM G173, titled Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface, provides standardized solar spectral irradiance tables for reference use. Its purpose is to define commonly used solar spectral conditions in a controlled, repeatable format. This makes the standard useful when a project needs a clear spectral basis for calculation, comparison, or evaluation. As an ASTM standard, it is typically used as a technical reference document rather than a performance specification.

Where is ASTM G173 used?

ASTM G173 is commonly used in solar energy work where reference irradiance data are needed for analysis or testing. It may support photovoltaic and solar thermal evaluation, optical or spectral measurements, and simulation workflows that depend on consistent solar input values. The standard is also relevant when comparing equipment performance under defined reference conditions. In practice, ASTM G173 helps teams align calculations and test reports with a shared solar spectral basis.

Why is ASTM G173 important?

ASTM G173 is important because reference irradiance values affect how results are interpreted and compared. Using a recognized standard helps improve consistency across testing, product development, and technical documentation. It can also reduce disagreement in procurement or qualification work by giving all parties the same spectral reference. For engineering and quality control teams, ASTM G173 supports more reliable assessment of solar-related products and systems.

• Reference solar spectral irradiance tables
• Direct normal and hemispherical data
• 37° tilted surface reference conditions
• Solar testing and analysis support
• Consistent technical comparison basis