EN 208 applies to Visible lasers only (ie 400 – 700 nm wavelength range).
Standard protective eyewear generally has a high Optical Density (OD), for example OD 6 or higher is common, giving an attenuation factor 1,000,000 or more. The result is that even visible laser beams become invisible and we cannot see at what point the beam is landing.
From the point of view of safety it is better if we can tell where the beam is, since we are then less likely to expose ourselves to it. Also sometimes it is necessary to be able to see where the beam is for purposes of alignment.
- Balances the Optical Density between protection and visibility of the beam
- Protects against the beam in the case of accidental direct exposure to the eye
- Allows the wearer to see the spot from the beam
- Reduces the power of the laser beam to below the Class 2 limit (ie 1 mW for CW lasers)
- Is not designed for intentional direct viewing of the beam
EN 208 (Personal eye-protection. Eye-protectors for adjustment work on lasers and laser systems (laser adjustment eye-protectors)) specifies testing and markings for laser alignment eyewear. To calculate the required eyewear specification for alignment eyewear for your laser, do the following:
For CW lasers (and pulsed lasers with pulse durations greater than 0.2 ms)
Take the CW (or average) power of the laser (if the beam is larger than 7 mm take only the power which can pass through a 7 mm diameter aperture)
Look up the specification from table B1.
For Pulsed lasers (with pulse durations between 1 ns and 0.2 ms)
Take the Energy per pulse (for beams exceeding 7 mm take the Energy passing through a 7 mm diameter aperture)
Multiply by correction factor N1/4 (where N is the number of pulses in 10 s)
Look up specification from table B1 below.
|Scale Number||Maximum Power
(Duration > 2 x 10-4 s)
(Pulses 10-9 to 2 x 10-4 s)
|RB1||0.01||2 x 10-6|
|RB2||0.1||2 x 10-5|
|RB3||1||2 x 10-4|
|RB4||10||2 x 10-3|
|RB5||100||2 x 10-2|
Hence eyewear is marked as follows:
Eg. 532 0,1 W 2 x 10-5 J R2
It is important not to confuse RB2 EN208 marking with R LB2 EN207 marking etc.
Eyewear with EN208 markings will have an Optical Density at the specified wavelengths, as shown in this table:
|Scale Number||Optical Density|
|RB1||1 > OD < 2|
|RB2||2 > OD < 3|
|RB3||3 > OD < 4|
|RB4||4 > OD < 5|
|RB5||5 > OD < 6|
EN208 specifies an extensive list of testing similar to EN207. In Particular the damage threshold testing is carried out using a beam size of 1 mm2, ie 10-6 m2)