Introduction to EN 171 Standard – Infrared (IR) Protection for Eye Protection
1. Overview of EN 171 Standard
- Full Name: EN 171 – Personal Eye Protection: Infrared (IR) Filters
- Purpose: Specifies the requirements for infrared (IR) protection filters used in personal eye protection.
- Scope: Covers all types of protective eyewear used in IR-intensive environments, including:
- Safety glasses
- Safety goggles
- Face shields
- Welding visors
- Specialty lenses used in high-temperature industries
The EN 171 standard ensures that protective lenses effectively filter harmful infrared radiation (IR-A, IR-B, IR-C) while maintaining good optical clarity and preventing heat damage to the eyes.
2. Importance of Infrared (IR) Protection in Eye Safety
Infrared radiation (IRR) is emitted by:
- High-temperature sources (furnaces, molten metal, glass manufacturing)
- Welding and cutting operations
- Lasers and industrial heating systems
Risks of IR Exposure to the Eyes:
🔴 Thermal burns on the cornea and retina
🔴 Cataract formation (long-term exposure)
🔴 Retinal damage leading to vision loss
🔴 Eye strain and discomfort from excessive heat
EN 171 ensures that lenses block excessive IR radiation while allowing sufficient visible light for safe work operations.
3. Key Requirements of EN 171
The EN 171 standard sets strict guidelines for infrared protection levels, ensuring that safety eyewear:
✅ Effectively filters IR-A (780-1400 nm), IR-B (1400-3000 nm), and IR-C (3000 nm and above)
✅ Prevents excessive heat transmission to the eyes
✅ Maintains optical clarity with minimal distortion
Infrared protection is measured on a scale of 1.2 to 10, where higher numbers indicate stronger IR filtering and lower light transmission.
Infrared Protection Scale (EN 171 Marking)
| Scale Number | IR Protection Level | Light Transmission (%) |
|---|---|---|
| 4-1.2 | Low IR protection | 74.4 – 100% |
| 4-1.4 | Moderate IR protection | 65.2 – 74.4% |
| 4-1.7 | High IR protection | 57.2 – 65.2% |
| 4-3 | Very high IR protection | 22.4 – 29.1% |
| 4-4 | Industrial IR protection | 12.0 – 22.4% |
| 4-5 | Foundry-level IR protection | 5.0 – 12.0% |
| 4-6 | Heavy-duty IR protection | 2.0 – 5.0% |
| 4-7 | Extreme IR protection | 0.1 – 2.0% |
- Lower numbers (4-1.2, 4-1.4): Suitable for moderate heat exposure in industrial settings.
- Higher numbers (4-6, 4-7): Required for foundry work, glassblowing, and welding.
4. Testing Methods in EN 171
EN 171 defines specific test methods to ensure that lenses meet IR protection requirements while maintaining high optical quality. The key tests include:
- Infrared Transmission Test (IR Filtering Efficiency)
- Luminous Transmission Test (Visible Light Passing Through)
- Optical Quality & Distortion Test
- Heat Resistance Test
- Material Durability Test (Aging & Stability Under IR Exposure)
A. Infrared Transmission Test (IR Filtering Efficiency)
Purpose
- Measures how much IR radiation is blocked by the lens.
- Ensures the filter meets the required infrared protection scale.
Test Procedure
- A controlled infrared light source (780-3000 nm) is directed through the lens.
- A spectrophotometer measures the amount of IR radiation passing through.
- The transmission values are compared to the standard’s IR protection scale.
Pass/Fail Criteria
- Lenses must block at least 99% of IR-C radiation and meet the IR transmission limits for their respective scale number.
B. Luminous Transmission Test (Visible Light Passing Through)
Purpose
- Ensures that lenses provide sufficient visible light transmission while filtering IR.
- Prevents lenses from being too dark, which could affect workplace safety.
Test Procedure
- A white light source (simulating daylight) is directed through the lens.
- A photometer measures how much visible light passes through.
- The transmission percentage is compared to EN 171 requirements.
Pass/Fail Criteria
- Luminous transmission must fall within the defined range for each IR protection scale number.
C. Optical Quality & Distortion Test
Purpose
- Ensures that IR-filtering lenses do not introduce blurriness, visual distortion, or eye strain.
Test Procedure
- The lens is examined using an optical bench with a grid pattern behind it.
- The wearer looks through the lens to check for image distortion, blurring, or waves.
Pass/Fail Criteria
- The image must remain clear and undistorted.
D. Heat Resistance Test
Purpose
- Ensures that the lens does not degrade, warp, or melt under high temperatures.
Test Procedure
- The lens is exposed to a heat source at 100°C for 10 minutes.
- The lens is checked for warping, cracking, or material degradation.
Pass/Fail Criteria
- The lens must maintain its structural integrity and optical properties.
E. Material Durability Test (Aging & Stability Under IR Exposure)
Purpose
- Evaluates whether prolonged IR exposure causes material degradation (yellowing, brittleness, cracking).
Test Procedure
- The lens is exposed to intense IR radiation (780-3000 nm for 50 hours).
- The lens is checked for discoloration, cracking, or loss of IR protection properties.
Pass/Fail Criteria
- The lens must maintain its IR-blocking properties and optical clarity after prolonged exposure.
5. Marking & Certification of EN 171 Eyewear
Once an IR-protective lens passes EN 171 tests, it is certified and marked accordingly.
EN 171 Marking System
- IR Filter Scale Number (e.g., 4-1.2, 4-6)
- Optical Class (1, 2, or 3, indicating distortion levels)
- Manufacturer’s Mark (e.g., “Uvex,” “Bolle”)
- CE Marking (Compliance with EU Safety Standards)
For example, “4-4 1 CE” means:
- IR Filter: 4-4 (Industrial-level IR protection)
- Optical Class: 1 (highest optical quality)
- Certified for European safety regulations (CE mark)
6. Comparison with Related Standards
| Standard | Focus | Key Features |
|---|---|---|
| EN 166 | General Eye Protection | Covers optical & mechanical safety |
| EN 167 | Optical Test Methods | Tests clarity, refraction, and lens quality |
| EN 168 | Non-Optical Test Methods | Evaluates heat, impact, and chemical resistance |
| EN 170 | UV Protection | Defines UV-filtering requirements |
| EN 171 | IR Protection | Defines IR-filtering requirements |
| EN 172 | Solar Protection | Specifies sun glare protection for industrial eyewear |
7. Conclusion
The EN 171 standard is essential for ensuring that protective eyewear provides adequate infrared (IR) protection while maintaining high optical quality. Its strict testing methods guarantee heat-resistant, durable, and distortion-free eye protection in high-temperature environments.
