Laser Alignment (Adjustment Eyewear) – European Standard EN 208

EN 208 applies to Visible lasers only (ie 400 – 700 nm wavelength range).

Standard protective eyewear has a high Optical Density (OD), for example, OD 6 or higher is common, resulting in an attenuation factor of one million or more. As a result, even visible laser beams become invisible, and we cannot see where the beam is landing.

From a safety standpoint, knowing where the beam is is preferable because we are less likely to expose ourselves to it. It is also sometimes necessary to be able to see where the beam is for alignment purposes.

Alignment eyewear:

  • 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 laser alignment eyewear testing and markings. 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 laser’s CW (or average) power (if the beam is larger than 7 mm, only take the power that 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)
Maximum Energy
(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)