When a buyer asks for "UV stable" plastic and the supplier answers "tested 1,000 hours", the two sides are usually talking past each other. Hours mean nothing without the standard, the lamp and the cycle behind them. This guide explains what a uv weathering test astm g154 program actually runs, how it differs from xenon arc uv aging under ASTM G155, and how to read the reports suppliers send.
What a UV Weathering Test ASTM G154 Cycle Runs
ASTM G154 is the standard practice for fluorescent UV lamp devices — the QUV tester is the reference equipment. Two lamp types dominate. The uva-340 lamp simulates the 295-365 nm slice of daylight ultraviolet and is the realistic choice for most durability claims. UVB-313 pushes shorter, harsher wavelengths that accelerate damage quickly but can trigger failure modes that never appear in service, so it suits QC screening rather than qualification. The workhorse cycle is 8 hours of UV at 60°C black-panel temperature followed by 4 hours of condensation at 50°C, with irradiance held near 0.89 W/m²/nm at 340 nm. Moisture is the point of the condensation phase: UV plus heat plus water is what cracks and chalks surfaces, and a dry UV-only exposure predicts almost nothing useful.
The Variables to Pin Down
- Lamp type — UVA-340 for realistic claims, UVB-313 for harsh screening
- Irradiance setpoint and control mode — W/m²/nm at 340 nm, not just a timer
- Cycle — light and dark split, condensation or spray, black-panel temperature
- Duration and evaluation — hours to first visual change, plus retained-property checks
QUV Test Cycle vs Xenon Arc: Where Each Belongs
| Parameter | ASTM G154 (fluorescent UV) | ASTM G155 (xenon arc) |
|---|---|---|
| Light source | UVA-340 / UVB-313 fluorescent | Filtered xenon arc, full spectrum |
| Spectral coverage | UV only, abrupt cutoff | UV, visible and IR, close to sunlight |
| Moisture | Hot condensation, optional spray | Water spray plus RH control |
| Best at | Mechanical degradation, fast screening | Color and gloss correlation, full-sun simulation |
| Typical use | Formulation and QC comparison | Automotive, textiles, architectural coatings |
Xenon arc uv aging under G155 reproduces the full solar spectrum, which is why color-change and gloss-loss claims lean on it; a quv test cycle predicts chain scission and mechanical loss faster and more cheaply but reads color shift poorly. Neither standard defines pass or fail, so a supplier quoting "passed G154" without a duration and an acceptance criterion has told you nothing. For plastic parts the practical split is simple: screen formulations and compare lots on QUV, and move to xenon when the claim is about how the part looks after years of sun. Where outdoor correlation is needed, buyers ask for exposure data from a named site — Arizona for high irradiance and low humidity, Florida for irradiance with heavy moisture — alongside the lab hours: the lab test ranks formulations, the outdoor panel proves the ranking survives real weather.
Reading the Report: Hours Are Not Years
There is no universal acceleration factor. Published correlations for these methods run roughly 8 to 15 times depending on lamp, cycle and the exposure site being modelled — Florida humidity and Arizona dry irradiance age the same part differently — and the polymer’s own action spectrum decides which lamp is even relevant. Treat lab hours as a comparison tool between formulations, not a warranty or a service-life promise. Insist on the cycle table, the irradiance control record and the property-retention data behind any outdoor claim: the ASA vs ABS durability comparison shows how QUV hours are quoted for weather-resistant resins, the datasheet reading guide covers what weathering lines on data sheets mean, and our plastic materials hub and company directory connect buyers with resin and compounder partners.
