Differences between xenon arc lamps, carbon arc lamps, and UV lamps in automotive interior and exterior light aging tests

Rationale

In the photoaging test of automotive interior and exterior materials, xenon lamp, carbon arc lamp and ultraviolet lamp are the three commonly used accelerated aging light sources. They both simulate the ultraviolet part of natural daylight, but there are significant differences in the luminescence mechanism and spectral distribution. Xenon lamps produce a continuous spectrum through ionized xenon gas, covering the ultraviolet, visible and infrared regions, which can comprehensively simulate solar radiation. The carbon arc lamp uses the arc discharge between the carbon rod electrodes to emit light, and its spectrum has a strong linear spectrum in the ultraviolet region. UV lamps mainly rely on fluorescence or mercury vapor discharge, and the emission spectrum is concentrated in the ultraviolet band, especially in the UV-A and UV-B regions. From the perspective of radiation mechanism, the spectral continuity of xenon lamps is closer to natural light, while the spectra of carbon arc lamps and ultraviolet lamps are more selective.

Spectral distribution vs. simulation realism

The spectral distribution directly affects the authenticity of material aging. Xenon lamps can adjust the spectrum through filters to match the sun's spectrum in different regions or environments, such as using daylight filters to simulate direct sunlight or window pane filters to simulate sunlight through glass. In addition to the continuous background, there are obvious UV spikes in the spectrum of carbon arc lamps, especially in the wavelength band below 295 nm, which is very rare in ground sunlight, which may lead to uncommon degradation of materials under natural conditions. The spectrum of UV lamps is highly concentrated in the ultraviolet region, such as the main peak of UV-A lamps at about 340 nm or 365 nm, and the main peak of UV-B lamps at about 313 nm. Overall, xenon lamps have an advantage in simulating full-spectrum sunlight, with carbon arc lamps potentially introducing atypical UV radiation and UV lamps focusing on the aging effects of UV bands.

Test conditions

The test conditions of the three light sources have their own emphasis. Xenon lamp tests usually control irradiance, blackboard temperature, cabinet temperature and relative humidity, and can set light and dark cycles and spray cycles to simulate day and night alternation and rain erosion. Irradiance control is controlled by multiple reference standards such as ISO 4892-2, and the common wavelength range is set at 300 nm to 400 nm or 340 nm. The test parameters of carbon arc lamps are similar, but due to their spectral characteristics, irradiance control is often based on specific wavelengths, and carbon rods need to be replaced regularly to maintain stability. UV lamp testing mainly controls ultraviolet irradiance and condensation or spray conditions, and the test cycle is usually carried out alternating between UV irradiation and condensation, such as referring to ASTM G154 or ISO 4892-3. In terms of parameter controllability, xenon lamp systems usually integrate more comprehensive sensors and feedback mechanisms, making it easier to accurately simulate complex environments.

Impact on automotive interior and exterior materials

The influence paths of different light sources on material aging are different. Automotive interior materials such as dashboards and seat fabrics are often exposed to sunlight through glass, so xenon lamps and window glass filters can better simulate their use environment, mainly causing color changes, loss of gloss and polymer embrittlement. Exterior materials such as bumpers and car paint are exposed to full-spectrum sunlight, and xenon lamps can simulate their combined photothermal aging, resulting in fading, chalking and mechanical properties. Carbon arc lamps may accelerate the embrittlement of some plastics (such as polypropylene) due to strong UV spikes, but may be less correlated with actual outdoor aging. UV lamps are mainly used to evaluate the resistance of materials to UV rays, such as rapid screening of coating weather resistance, but their lack of thermal effect may underestimate the performance degradation of materials in actual use. The difference in material response can be quantified by aging indicators, such as the formula for calculating the color difference ΔE: ΔE = √ (ΔL² + Δa² + Δb²), where L, a, and b are the Lab color space coordinates.

Standard compliance

Light source selection takes into account standard compliance. International standards such as ISO, ASTM and the national standard GB/T all stipulate the application scope of different light sources. For example, ISO 4892-2 describes in detail xenon exposure methods for a wide range of plastics and coatings; ISO 4892-3 is for UV fluorescent lamp methods. The carbon arc lamp method is common in historical standards, such as JIS D0205, but has been gradually replaced by xenon lamps in recent years. When choosing, it is necessary to weigh the material type, the environment in which it will be used, and the evaluation goals: if you are looking for a high correlation with natural aging, xenon lamps are usually the first choice; If you focus on the impact of the UV band or perform rapid screening, UV lamps are more economical; Carbon arc lamps may be used for specific traditional tests or historical data comparison. The following comparison can be referred to when making decisions:

Summary

Xenon lamps, carbon arc lamps and ultraviolet lamps have their own characteristics in the light aging test of automobile interior and exterior decoration. Xenon lamp has a comprehensive spectrum and high controllability, suitable for simulating comprehensive aging in a real environment; There are atypical UV spikes in the carbon arc lamp spectrum, which may affect the correlation of the experiment. UV lamps focus on the UV band and are suitable for rapid screening. In practical applications, the light source should be reasonably selected according to the material performance requirements, standard regulations and test purposes, and combined with other environmental factors such as temperature and humidity for comprehensive evaluation to accurately predict the weather resistance of the material.

References

International Organization for Standardization. Plastic laboratory light source exposure method Part 2: Xenon arc lamp. ISO 4892-2.

American Society for Testing and Materials. Operating standards for non-metallic materials xenon arc lamp exposure equipment. ASTM G155.

International Organization for Standardization. Plastic Laboratory Light Source Exposure Method Part 3: Fluorescent UV Lamp. ISO 4892-3.

Japanese Industrial Standards. Weather resistance test method of auto parts. JIS D0205.