ASTM G24: Simulating Real-World Sunlight Exposure Behind Glass
ASTM G24 provides a standardized method for evaluating how nonmetallic materials withstand sunlight that passes through glass—conditions commonly found in environments like vehicle interiors or architectural windows. This practice provides a reliable way to simulate and compare real-world degradation effects caused by solar radiation, temperature, and humidity while controlling for environmental variability. By using an enclosed cabinet design, the test helps manufacturers and researchers assess material performance and durability in under-glass exposure conditions.
Key Test Parameters
Exposure Environment
- Natural sunlight filtered through a glass cover (not direct exposure like ASTM G7).
- Designed to simulate indoor or under-glass environments such as vehicle interiors or behind building windows.
- Conducted outdoors where the cabinet receives unobstructed sunlight throughout the day.
Exposure Apparatus
- Type A (Ventilated): Allows passive air circulation over specimens. Simulates moderate temperature under-glass environments.
- Type B (Black Box / Non-ventilated): Fully enclosed with black-painted exterior to absorb heat. Simulates high-temperature under-glass conditions (e.g., car dashboards).
- Temperatures may exceed 80 °C under strong sunlight.
Glass Specifications
- Transparent, non-laminated, “greenhouse-quality” flat glass (2–3.2 mm thick).
- Pre-aged by 3 months of outdoor exposure to stabilize UV transmittance.
- Typical UV transmittance after pre-aging:
- ~10–20% at 320 nm
- ≥85% at ≥380 nm
Mounting and Orientation
- Specimens mounted parallel to the glass, approximately 75 mm below it.
- Orientation toward the equator at tilt angles between 5° and 45°, or other agreed-upon configurations.
- Can also use tracking mounts to maintain a normal angle to the sun.
Measurement and Monitoring
- Solar radiant exposure is measured via pyranometer or radiometer.
- Air and specimen temperatures, relative humidity, and solar energy are recorded daily.
- Optional UV-only radiant exposure measurements (like UVB) can be recorded.
Exposure Duration / Endpoints
Exposure continues until one of the following:
- A specified solar radiant exposure dose is reached (typically in J/M²).
- A predetermined material change (color shift, gloss loss, strength change) occurs.
- A set exposure time (months or years) is completed.
Control Material
As with all weathering tests, at least one material of known performance should be tested alongside the samples to benchmark performance. Preferably, a control material with known high durability and one with poor durability should be used.
Why Test to ASTM G24
ASTM G24 provides valuable insight into color stability, gloss retention, and overall durability under realistic indoor or under-glass environments. By following a standardized, repeatable method, ASTM G24 testing helps predict long-term appearance changes, supports product quality claims, and ensures materials meet customer and industry expectations for UV and heat resistance. This standard is closely related to ASTM G7, which specifies natural outdoor exposures with direct sunlight.
Pros and Cons of ASTM G24
- Inexpensive
- Like all outdoor testing, ASTM G24 is an inexpensive option that provides valuable benchmark data
- Realistic Testing Conditions
- Natural outdoor testing provides the most accurate and realistic testing environment - the true answer to make sure your accelerated laboratory tests are appropriate
- Customizable options
- ASTM G24 allows for customized exposure glass options tailored towards your testing needs
- Long testing duration for durable materials
- Although outdoor testing gives true results regarding in-service performance, some users may prefer accelerated testing for faster results, though that should always be validated with outdoor data
Q-Lab's Natural Outdoor Weathering Test Facilities
Q-Lab offers outdoor exposure testing programs, including under glass testing to ASTM G24 and direct exposures according to ASTM G7, at our internationally-recognized, ISO 17025-accredited benchmark locations in Florida and Arizona. Weathering exposures at these sites are not only realistic; they also could be considered a form of accelerated weathering testing (depending on where the product will be used outdoors) and are the best way to verify laboratory test results. Q-Lab also provides all users with climate data to enhance interpretation of data collected during outdoor exposures. See our Outdoor Testing brochure for more information on these sites and our Testing Services brochure to learn about our full range of weathering testing services.
More ASTM G24 Resources
Standards
Review setup and performance information on key international and OEM test standards from ASTM, ISO, SAE, JIS, GB, and more.
Document Library
Browse Q-Lab’s extensive library of weathering testing literature and technical content.
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