EN 207, CE Marking and Laser Protective Eyewear
Where a relevant European Directive exists, all products sold in the European Union must bear the CE mark. It is illegal to sell non-CE marked products. This means that laser safety eyewear must meet the laser protection requirements of the Personal Protective Equipment (PPE) Directive. While manufacturers can use their own standard to demonstrate compliance with the directive in theory, as long as they can demonstrate that their standard is sufficiently rigorous, in practice the eyewear is always tested and certified to EN 207 1 (or EN 208 2 for alignment eyewear). Such testing must be performed by a government-approved testing facility; self-certification is not permitted for these standards. As a result, since 1997, when EN 207 became a harmonized European Standard, all legally sold laser protective eyewear in Europe has been certified to EN 207 or EN 208.
Despite being in use since 1997, EN 207 is frequently misunderstood. As a result, we are providing a brief explanation here to assist users of laser safety eyewear.
Optical Density Specification
Prior to EN 207, laser protective goggles were typically specified by their Optical Density (OD), and this is still a popular method, particularly in the United States (where Optical Density is frequently the only protective information available for the eyewear). The optical density (OD) of eyewear is defined as the log of the attenuation factor at a given wavelength. Thus, eyewear with a factor of 1,000,000 attenuation of Nd:YAG laser radiation has an OD of 6 at 1064 nm. The optical density method for specifying eyewear involves calculating the maximum accessible emission from the laser and dividing it by the Maximum Permissible Exposure (MPE)3 for laser radiation. This number’s log represents the minimum required OD for the eyewear.
Limitations of Optical Density Specification
Consider a high power CO2 laser emitting at 10600 nm and some polycarbonate eyewear with an OD > 6 at the same wavelength. The Class 1 Accessible Emission Limit for this wavelength is 10 mW, so this power is safe under all exposure conditions. As a result, we might anticipate that the eyewear will shield us from 1,000,000 x 10 mW = 10 kW of CO2 laser energy. However, when we expose the eyewear to a CO2 laser beam of even a few hundred watts, we find that it is quickly destroyed and provides little protection (even a 20 W beam will cause immediate burning of the eyewear).
As a result, we can see that optical density alone does not account for the damage threshold of the material used to protect us from laser radiation, i.e. the power or energy density (W/m2 or J/m2) that the eyewear can withstand. EN 207 was written to address this issue and takes both the Optical Density and the damage threshold of the eyewear into account.
EN 207 Markings Explained
Following EN 207 testing, the laser protective eyewear is given various markings that are printed on the eyewear and specify the maximum power and energy densities that the eyewear can protect against at different wavelengths.
The EN207 standard was updated in 2010, and the L rating was renamed LB. The calculations used to determine the required ratings have been slightly altered, so older eyewear will have L markings and newer eyewear will have LB markings, but the protection provided by L and LB ratings is nearly identical. For instance eyewear may be marked as follows:
- DI 750 – 1200 LB5
- R 750 – 1200 LB6
- M 750 – 1200 LB4
This means that over the wavelength range 750 – 1200 nm the eyewear has the following ratings:
D LB5 I LB5 R LB6 M LB4
The D, I, R and M refer to CW or different pulse lengths as follows:
- D – Continuous Wave (CW)
- I – Pulsed with pulse length > 1 µs and < 250 ms ‘Long Pulse’
- R – Pulsed with pulse length > 1 ns and < 1 µs, ‘Q-switched’
- M – Pulsed with pulse length < 1 ns, ‘Femtosecond’4
The ‘LB numbers’ (LB5, LB6, LB4, and so on) refer to the maximum power or energy density for which the eyewear is designed. The actual values must be obtained from Table B1 in EN 207 (which we cannot reproduce here due to copyright reasons). For the above-mentioned eyewear markings, the values are:
- CW – 1 MW/m2 D LB5
- Long Pulse – 500 J/m2 I LB5
- Q Switched – 5 kJ/m2 R LB6
- Femtosecond – 1.5 J/m2 M LB4
A one-order-of-magnitude increase in the LB number raises the power and energy density values by one order of magnitude. It should be noted, however, that EN 207 divides the LB number table into three wavelength ranges: 180-315 nm, 315-1400 nm, and 1400-1,000,000 nm. The above-shown relationship between LB numbers and power / energy densities applies only to the 315-1400 nm wavelength range. EN 207 is the standard for other wavelengths.
LB Numbers and Optical Density
In order to protect, the filter must be able to withstand the power of the laser beam without being destroyed, as well as attenuate the laser beam. To receive an LB rating during EN 207 testing, a filter must have an Optical Density greater than the LB number at the specified wavelength. As a result of the preceding example, we can conclude that the eyewear has an OD > 6 across the wavelength range 750 – 1200 nm (due to an RLB6 rating across this wavelength range). However, we don’t have to worry about calculating the MPEs and accessible emission because this has already been factored into the maximum power / energy densities specified for each LB number.
Specifying Eyewear Using EN 207
To specify appropriate LB numbers for your laser, do the following:
- Determine the smallest possible laser beam diameter to which a person could be exposed under reasonably foreseeable conditions.
- Determine the beam’s cross-sectional area at this point.
- Divide the laser’s average power by the beam area to get the average power density at this point.
- Look up the required LB number in EN 207’s Table B1. This number should be followed by a D.
Additionally for pulsed lasers:
- Divide the energy per pulse by the beam area to get the energy density5.
- Calculate a corrected energy density for lasers in the wavelength range 400-1400 nm by multiplying the actual energy density5 by N0.25, where N is the total number of pulses in 10 seconds.
- Look up the required LB number in EN 207 using the energy density5 or corrected energy density5. Precede this with an I for long pulse, R for Q-switched, and M for femtosecond or picosecond lasers.
Thus a 532 nm laser emitting 1 mJ, 7 ns pulses at 10 kHz, and having a minimum accessible beam diameter of 2 mm would require eyewear with the following minimum specification:
- D 532 LB6 (corresponding to 10 MW/m2)
- R 532 LB7 (corresponding to 50 kJ/m2)
To ensure that the eyewear is suitable for the laser, it must have both the correct I, R, or M specification (depending on the pulse length) and the correct D specification for pulsed lasers.
NB: The purpose of this article is to help laser users, Laser Safety Officers, and Laser Protection Advisers better understand EN 207. It is not meant to be an exhaustive examination of the subject. For more information, consult the Standard or contact Lasermet.
- EN 207 Personal eye-protection. Filters and eye-protectors against laser radiation (laser eye-protectors)
- EN 208 Personal eye-protection. Eye-protectors for adjustment work on lasers and laser systems (laser adjustment eye-protectors)
- Given by Table A1 and A2 in EN 60825-1 : 2007
- In actual fact picosecond pulses are also included.
- Peak power density must be calculated for lasers with pulse lengths less than 1 ns and wavelengths other than 315 – 1400 nm.