* Optical density, or O.D. as is it is commonly known, refers to the attenuation factor of the filter to the base 10. Therefore, a filter with an OD of 2 attenuates the laser by a factor of 10 to the 2nd or 100, an OD of 3 attenuates the laser beam by a factor of 1,000, an OD of 4 by a factor of 10,000.
* Visible Light Transmission, or VLT as it is commonly known, refers to the attenuation of light by a filter in the visible spectrum. It is commonly expressed as the percentage of the visible daylight spectrum light allowed to pass thru.
* Central Europe Certified, or CE refers to products sold in the European Union that must be CE marked where a relevant European Directive exists.