Safety glasses are rated according to their optical density (OD) in a given wavelength range. The OD scale is logarithmic, and measures the amount of light that can be transmitted through the lenses (see table below):
When choosing safety glasses, it’s necessary to consider the type of laser you’re using (CW or pulsed), the wavelength of the laser, output power, pulse energy, repetition rate, beam size, and exposure duration. A good rule of thumb is to make sure the OD of the safety glasses transmit an amount of laser radiation that is less than the Maximum Permissible Exposure at that wavelength (highest laser power density that is considered safe for the human eye). Always consult your laser safety officer when choosing the appropriate safety glasses for your laser application.