EN 207, CE Marking and Laser Protective Eyewear
All products sold in the European Union must be CE marked where a relevant European Directive exists. To sell non-
Despite being around for since 1997 EN 207 is still often not well understood. Consequently we are writing a brief explanation here to help users of laser safety eyewear.
Optical Density Specification
Prior to EN 207 laser protective goggles were usually specified by their Optical Density (OD) and this is still a widely used method especially in the USA (where Optical Density is often the only protective information available for the eyewear). The OD of eyewear is the log of the attenuation factor at a given wavelength. Thus eyewear which attenuates Nd:YAG laser radiation by a factor of 1,000,000 has an OD of 6 at 1064 nm. The method for specifying eyewear using optical density involves working out the maximum accessible emission from the laser and dividing it by the Maximum Permissible Exposure (MPE)3 for the laser radiation. The log of this number is the minimum required OD for the eyewear.
Limitations of Optical Density Specification
The problems with this approach are graphically illustrated if we consider a high power CO2 laser emitting at 10600 nm, and some polycarbonate eyewear having an OD > 6 at the same wavelength. The Class 1 Accessible Emission Limit for this wavelength is 10 mW and this power is therefore safe under all exposure conditions. We might therefore expect that the eyewear will protect us against 1,000,000 x 10 mW = 10 kW from the CO2 laser. However, if we place the eyewear in a CO2laser beam of even a few hundred watts we find that it is very quickly destroyed and offers little protection (even a 20 W beam will cause immediate burning of the eyewear).
So we see that Optical Density alone does not take account of the damage threshold of the material which is used to protect us from the laser radiation -
EN 207 Markings Explained
After testing to EN 207 the laser protective eyewear is awarded various markings which are printed on the eyewear and specify the maximum power and energy densities which the eyewear can protect against at different wavelengths. For instance eyewear may be marked as follows:
DI 750 -
R 750 -
M 750 -
This means that over the wavelength range 750 -
D L5 I L5 R L6 M L4
The D, I, R and M refer to CW or different pulse lengths as follows:
The 'L numbers' (L5, L6, L4 etc) refer to the maximum power or energy density which the eyewear is specified for. The actual values must be looked up from Table B1 in EN 207 (which for copyright reasons we cannot reproduce here). For the eyewear markings given above, the values are:
Long Pulse -
Q Switched -
An increase in the L number by 1, will increase the power and energy density values by one order of magnitude. Note however, that EN 207 breaks down the L number table into three wavelength ranges, 180 -
L Numbers and Optical Density
As well as being able to withstand the power of the laser beam without being destroyed, the filter must also be able to attenuate the laser beam in order to protect. During the EN 207 testing, in order for a filter to be given an L rating, the filter must have an Optical Density in excess of the L number, at the specified wavelength. Therefore, in the example shown above, we can deduce that the eyewear has an OD > 6 across the wavelength range 750 -
Specifying Eyewear Using EN 207
To specify appropriate L numbers for your laser, do the following:
Determine the minimum laser beam diameter to which a person might be exposed under reasonably foreseeable circumstances.
Calculate the cross-
iCalculate the average power density at this point by dividing the average power of the laser by the beam area
Look up the required L number from Table B1 in EN 207. Preceed this number with a D.
Additionally for pulsed lasers:
Calculate the energy density5 by dividing the energy per pulse by the beam area.
For lasers in the wavelength range 400 -
Using the energy density5 or corrected energy density5 as appropriate, look up the required L number from Table B1 in EN 207. Precede this with an I for long pulse, R for Q-
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 L6 (corresponding to 10 MW/m2)
R 532 L7 (corresponding to 50 kJ/m2)
Note that for pulsed lasers the eyewear must have both the correct I, R or M specification (depending on the pulse length) and the correct D specification, to ensure that it is suitable for the laser.
Alternative means of obtaining the L number specification are to use the LaserSafe PC software, or to ask the advice of the Lasermet sales staff.
NB: This article is intended to help laser users, Laser Safety Officers and Laser Protection Advisers gain a better understanding of EN 207. It is not intended as an exhaustive study of the subject. For more information refer to the Standard or call Lasermet to discuss.
EN 207 Personal eye-
EN 208 Personal eye-
Given by Table A1 and A2 in EN 60825-
In actual fact picosecond pulses are also included.
For lasers with pulse lengths less than 1 ns and a wavelength outside the range 315 -