When evaluating a UV tester, prioritize the Irradiance Control System. High-end models feature 'Eye-On' or solar eye sensors that automatically maintain light intensity. Ensure the device uses standardized UVA-340 or UVB-313 lamps, as these simulate different sunlight conditions. Additionally, check for Black Panel Temperature (BPT) control range (typically 30°C to 90°C) and water spray/condensation functions to simulate rain and dew, which are critical for realistic material degradation testing.