It is your personal responsibility to ensure you are wearing the correct eye protection at all times for the appropriate wavelength(s) within the Nominal Hazard Zone. Information here is given for guidance only, you must attend the laser safety workshop and complete the online assessment.
The LB Rating Specifies not just the attenuation of the filter but also the damage threshold of the material - Maximum power or energy density withstanding a direct hit period of 5 seconds (CW) or for 50 pulses.
T - transmission percent
D - Continuous Wave (CW) > 250 ms
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, 'Mode locked'
OD - The filter will have an Optical Density in excess of the LB number, therefore the OD is inherent in the LB rating.
Example: 10w CW laser of 532nm wavelength, beam diameter of 4mm and power density = 8x105 W/m² will require eye protection rated at LB5 as the power density is close to 106 W/m² and you should always round up to the value that provides more attenuation of the beam.
Table of Protection Levels per the European standard EN 207
When purchasing glasses for a particular laser you can consult with your laser safety officer or request the supplier to help you choose the correct ones. They will need information on the type of laser, emmision type (pulsed or continuous wave), wavelength range, the beam diameter and divergence as well as the average power or peak energy per pulse. They can then calculate from this information the correct LB numbers for you.
Sample labelling on laser protection eyewear