---
title: What is the difference between QFS-40 and UVB-313EL Lamps?
description: QFS-40 and UVB-313EL lamps are both used in QUV accelerated weathering testers to provide fluorescent UV light that includes a significant UVB component for faster testing. The diagram below shows that both have similarly-shaped spectral power distributions. How do these lamps differ, and which one is best for use in your QUV?
image: https://blog.q-lab.com/hubfs/Blog/difference_QFS-40_UVB-313EL_Lamps.jpg
---
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# What is the difference between QFS-40 and UVB-313EL Lamps?
Posted by [Andy Francis](https://blog.q-lab.com/author/andy-francis) on Jul 16, 2020 10:39:16 AM
QFS-40 and UVB-313EL lamps are both used in QUV accelerated weathering testers to provide fluorescent UV light that includes a significant UVB component for faster testing. The diagram below shows that both have similarly-shaped spectral power distributions. How do these lamps differ, and which one is best for use in your QUV?
The QFS-40 lamp was developed to meet the specifications of SAE J2020, which, when written, had a hardware-specific requirement to use this lamp. That hardware-specific requirement has been removed in SAE J2020 and in most standards that are based on SAE J2020.
UVB-313EL lamps were developed later, and operate with the QUV’s SOLAR EYE irradiance control system to provide a more consistent and repeatable level of irradiance than using QFS-40 lamps in a QUV/basic, due to lamp aging, maintenance, and environmental conditions. UVB-313EL lamps are significantly less expensive than QFS40 lamps because far greater volumes of UBV-313EL are manufactured.
If your QUV has SOLAR EYE irradiance control, you should use UVB-313EL lamps and set the irradiance to 0.48 W/m2 at 310 nm for SAE J2020 and standards based on it, even if those standards have not been updated to include the UVB-313 lamp. This is the most cost-effective and best-performing option when irradiance control is available.
If your QUV does not have irradiance control (QUV/basic or old style models), you should continue to use QFS-40 lamps to maintain comparable irradiance levels to what is intended by a test standard or historical practice. UVB‑313EL lamps used in QUV testers without irradiance control will generate irradiance that is significantly higher than QFS-40 lamps in the same tester.
Topics: [Weathering](https://blog.q-lab.com/topic/weathering?hsLang=en), [FAQ](https://blog.q-lab.com/topic/faq?hsLang=en), [QUV](https://blog.q-lab.com/topic/quv?hsLang=en)
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