PV Testing Essentials | Analysis of UV Lamp Attenuation

Analysis of UV Lamp Attenuation

As PV laboratories and module manufacturers place increasing emphasis on the accuracy of IEC standard testing, the reliability of UV aging test equipment has become a key topic in the industry.

The aging and lifespan of UV lamps are critical factors affecting testing accuracy and long-term operational cost.

This article explores how UV lamps gradually attenuate during continuous operation — and why understanding this phenomenon matters.

1. Introduction

With the rapid development of the global photovoltaic industry,
the long-term reliability of PV modules has become a decisive factor influencing both power generation efficiency and levelized cost of electricity (LCOE).

During outdoor operation, PV modules are subjected to multiple environmental stress factors such as UV radiation, high temperature, humidity, thermal cycling, sand abrasion, and salt-mist corrosion.

Among these, ultraviolet (UV) radiation plays a particularly critical role in material degradation.
It accelerates the yellowing and cracking of encapsulant films, reduces light transmittance, and leads to power degradation of the modules.

Therefore, the International Electrotechnical Commission (IEC) and other testing standards worldwide explicitly require accelerated UV aging tests for both module materials and complete PV modules to ensure their durability and reliability.

2. Introduction to the UV Aging Chamber

The IEC 61215 standard specifies clear requirements for the spectrum and irradiance levels used in UV testing.
The UV Aging Chamber is a specialized testing apparatus designed precisely according to these requirements.

This system generates ultraviolet radiation with a defined spectral and energy distribution using UV lamps, simulating long-term exposure conditions.
By continuously irradiating PV modules or material samples, it accelerates the aging process — allowing laboratories to evaluate weather resistance and reliability within a shorter testing period.

A standard UV Aging Chamber is composed of several core subsystems:

1. UV Light Source System – Various types of UV lamps are available in the market, including metal halide lamps, xenon lamps, and fluorescent lamps.
   Zealwe Tech adopts metal halide lamps as the primary light source for their stable performance and spectral conformity.

2. Light Source Control System – Each UV lamp’s power output is precisely regulated by an EPS power supply, ensuring consistent irradiance.

3. Irradiance Monitoring System – Real-time UVA and UVB data are collected through dedicated irradiance probes for accurate monitoring and calibration.

4. Temperature Control System – This subsystem maintains both chamber and sample temperature, reproducing real-world thermal conditions experienced by PV modules.

5. Software Control System – A fully integrated platform that manages all control and monitoring functions, providing intuitive operation and data visualization.

3. Emission Mechanism of UV Lamps

Metal halide ultraviolet (UV) lamps operate by filling the lamp tube with high-pressure inert gas (such as xenon) and metal halides (such as iron iodide and gallium bromide).

When a high-voltage electric field is applied, the gas becomes ionized and forms plasma. Electrons collide with metal atoms, exciting them to higher energy states.

These excited atoms are unstable and quickly return to lower energy levels or the ground state, releasing excess energy in the form of photons — primarily ultraviolet light.

By adjusting the types and proportions of metal halides inside the lamp, it is possible to generate UV radiation with specific wavelengths tailored to testing requirements.

During operation, however, the lamp’s spectral characteristics and irradiance are affected by gradual lamp attenuation.

As a metal halide lamp operates for long periods under high temperature, the filament metal slowly evaporates and deposits on the quartz wall, forming dark spots that reduce light transmittance and cause local overheating — leading to a decline in irradiance intensity.

In addition, as the lamp continues aging, the ionized materials (such as mercury vapor) inside the tube are gradually depleted, changing the discharge characteristics and lowering the overall luminous efficiency.

4. Long-Term Aging Test of UV Lamps

In this study, metal halide UV lamps were used as test samples.
Each lamp was operated at 80% of its rated output power to simulate long-term working conditions and to monitor irradiance stability over time.

An irradiance probe was fixed at a specific measurement point to continuously record irradiance intensity.
After 4,000 hours of operation, the irradiance decreased by approximately 44%, indicating significant attenuation during extended use.

However, since the output power of metal halide UV lamps can be adjusted via the EPS power supply, a compensatory approach was also tested.
Starting with an initial irradiance value at 80% output power, the test gradually increased the lamp power to 100% output over the same 4,000-hour period.
Under this condition, the irradiance attenuation was reduced to approximately 25%, demonstrating that power adjustment can temporarily mitigate light decay, though it cannot eliminate it entirely.

In addition to irradiance intensity, the UVB proportion within the total UV spectrum is another key indicator in UV aging tests.
After 4,000 hours, data showed that the UVB ratio increased from about 7% to over 10%.
This exceeds the IEC standard range, mainly because the UVA component decays faster than UVB as the lamp’s internal metal halide composition changes over time.
As a result, the spectral balance of the UV output shifts, which can impact test consistency and accuracy if not properly monitored.

5. Conclusion

During prolonged operation, metal halide UV lamps inevitably experience irradiance attenuation due to material evaporation and spectral shifts inside the lamp tube.
Although adjusting the power output through the EPS power supply can temporarily compensate for the decline in irradiance intensity, the loss of internal metal halide components is irreversible.
As a result, the UVB proportion gradually increases after approximately 3,000 hours, eventually falling outside the acceptable IEC test range.

Based on these findings, Zealwe Tech recommends replacing UV lamps every 3,000 hours of operation to ensure the accuracy, repeatability, and standard compliance of UV aging tests.

Looking ahead, Zealwe Tech will continue to refine its UV test systems, enhance spectral stability control, and support laboratories worldwide with reliable solutions that uphold testing precision and operational efficiency.