Detailed Introduction to EN 167 Standard
The EN 167 standard specifies the optical test methods for personal eye protection. It is part of the broader European standards for protective eyewear, ensuring that lenses and visors used in safety glasses, goggles, and face shields meet certain performance criteria in terms of optical quality, light transmission, and resistance to defects.
This standard is particularly important in industrial, medical, and laboratory settings, where workers rely on clear and accurate vision while using protective eyewear. It defines the requirements for testing optical properties such as refractive power, prismatic deviation, and light diffusion.
1. Overview of EN 167 Standard
- Full Name: EN 167 – Personal Eye-Protection: Optical Test Methods
- Purpose: Defines optical test methods for protective eyewear to ensure that they provide clear, undistorted vision and meet safety requirements.
- Scope: Applies to all types of protective eyewear, including:
- Safety glasses
- Goggles
- Face shields
- Welding filters
- Prescription safety lenses (when used in industrial settings)
The EN 167 standard is often used in conjunction with other standards, such as EN 166 (General Eye Protection Requirements) and EN 170 (Ultraviolet Filters).
2. Optical Requirements Tested Under EN 167
EN 167 establishes various test methods to assess the optical performance of protective eyewear. The key parameters tested include:
- Spherical, Astigmatic, and Prismatic Refractive Power
- Light Transmission and Diffusion
- Quality of Optical Materials (Imperfections & Uniformity)
Each of these tests ensures that the eyewear provides accurate vision without distortion and meets safety regulations.
3. Detailed Testing Methods in EN 167
The standard outlines specific test methods to measure the optical performance of protective eyewear. Below are the main tests and their procedures.
A. Spherical, Astigmatic, and Prismatic Refractive Power (Optical Clarity Test)
Purpose
- Ensures that lenses do not introduce distortion or blurriness that could affect the wearer’s vision.
- Important for tasks requiring precision, such as operating machinery or working with small objects.
Test Procedure
- Spherical Power Measurement (Focal Length Test)
- The focal power of the lens is measured using an optical instrument (such as a diopter meter).
- The lens must fall within the acceptable tolerance range of spherical refractive power.
- Acceptable limits depend on the optical class of the eyewear:
- Class 1: ±0.06 diopters (highest optical quality)
- Class 2: ±0.12 diopters
- Class 3: ±0.25 diopters
- Astigmatic Refractive Power Test
- Measures any distortion caused by astigmatism in the lens.
- Conducted using an optical bench where a beam of light is passed through the lens and the deviation is measured.
- Lenses must not introduce significant astigmatic distortion.
- Prismatic Deviation Test
- Tests whether the lens introduces any horizontal or vertical displacement in vision.
- Eyewear is placed in a prism compensator, and light deviation is measured.
- Strict tolerances apply to ensure that vision remains accurate and aligned.
Acceptable Limits
- High-quality optical lenses must meet strict limits on refractive power.
- Deviation beyond the standard limits can cause eye strain, headaches, and difficulty focusing.
B. Light Transmission and Diffusion Test
Purpose
- Ensures that safety lenses allow an appropriate amount of light to pass through.
- Prevents excessive diffusion (scattering) of light that could impair visibility.
- Important for environments with low or high lighting conditions.
Test Procedure
- Light Transmission Measurement
- A light source is directed through the lens, and a photometer measures how much light passes through.
- Acceptable range depends on lens type:
- Clear lenses: High transmission required (~85%-100%)
- Tinted or protective lenses (e.g., welding, UV protection): Transmission varies based on classification.
- Light Diffusion Test (Haze Test)
- Measures how much light is scattered within the lens.
- Excessive haze can cause blurred vision, reducing clarity.
- A haze meter or spectrophotometer is used to quantify the level of diffusion.
Pass/Fail Criteria
- Clear lenses should not significantly reduce light transmission or increase haze.
- Special protective lenses (such as welding or tinted lenses) must conform to their respective transmission categories.
C. Quality of Optical Materials (Imperfections & Uniformity Test)
Purpose
- Ensures that the lens material is free from defects that could impair vision.
- Detects imperfections such as bubbles, scratches, inclusions, or material inconsistencies.
Test Procedure
- Visual Inspection
- Lenses are examined under a controlled light source for any visible defects.
- Common defects checked:
- Scratches
- Bubbles or air pockets
- Waves or ripples in material
- Uneven thickness
- Optical Uniformity Test
- A beam of collimated light is passed through the lens.
- A reticle (grid pattern) is observed to check for distortions.
- Lenses must not introduce visual artifacts or optical distortions.
Acceptance Criteria
- Lenses must not have any defects that could impair visibility or cause eye strain.
- Special allowances may be made for tinted or coated lenses, as long as they do not affect clarity.
4. Marking & Certification
Once a lens passes the EN 167 tests, it receives certification and appropriate markings. The marking system follows the EN 166 standard, which includes:
- Optical Class:
- “1” (highest optical clarity, suitable for continuous use)
- “2” (moderate optical quality, for occasional use)
- “3” (lowest optical quality, short-term use only)
- Lens Type & Transmission Category:
- Clear, UV filtering, Infrared (IR) protection, welding shade, etc.
- Manufacturer’s Mark: Identifies the producer of the lens.
- European CE Marking: Indicates compliance with European safety standards.
5. Applications of EN 167
EN 167-compliant protective eyewear is used in various industries, including:
- Manufacturing & Construction: Protection from dust, debris, and impact.
- Medical & Laboratory Work: Clear vision for precision tasks.
- Welding & Metalwork: Specialized lenses for UV and IR protection.
- Military & Law Enforcement: Optical clarity for tactical gear.
- Aviation & Automotive: Eye protection for high-speed work environments.
6. Comparison with Related Standards
| Standard | Focus | Key Features |
|---|---|---|
| EN 166 | General eye protection | Includes optical & mechanical requirements |
| EN 167 | Optical test methods | Ensures clarity, transmission, and quality of lenses |
| EN 168 | Non-optical test methods | Covers resistance to chemicals, fogging, and aging |
| EN 170 | UV protection | Defines UV filtering requirements |
| EN 172 | Solar protection | Specifies sun glare filters for industrial use |
7. Conclusion
EN 167 plays a crucial role in ensuring that protective eyewear meets optical performance standards, providing users with clear, undistorted vision in hazardous environments. The testing methods defined in this standard help eliminate distortion, excessive light diffusion, and lens defects, ensuring that workers can perform their tasks safely and effectively.
