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Understanding Laser Safety Glasses Lens Specifications

The first thing is to decide on the appropriate lens filter requirements by considering the wavelength (nm) coverage, OD (Optical Density), Damage threshold (L ratings) and Visible Light Transmission (VLT).

Right lens (below) typically shows wavelengths covered, Optical densities OD and Visible Light Transmission.

Left lens (below) typically shows L Rating (damage threshold) Specifications and corresponding wavelengths

Some things to take into consideration:

  • Make sure that the lens filters you select will reduce possible exposure of the laser below the Maximum Permissible Exposure limit (MPE) Consider if you need to have visibility of the laser spot for alignment purposes, which is often the case for visible red lasers. In this case, the required Optical Density will need to be calculated precisely to provide a balance between visibility and protection.
  • Check the Visible Light Transmission of the filter or VLT. This is specified as a percentage and considers the response of the human eye to daylight. It gives a good indication of how light the glasses will be to look through. For example, if the VLT is less than 20% then it is best used in a well-lit environment.
  • The damage thresholds are specified in terms of L ratings. It requires that eyewear is labelled with protection levels that detail their damage thresholds, (e.g. 10600 D L5 (where L5 reflects a power density of 100 MegaWatt/m2 during a 10 seconds direct hit test at 10,600nm). The recomended scale numbers are shown in the below table.