Optical density, commonly abbreviated as OD, is a measurement used to describe how effectively laser safety lenses attenuate laser radiation.

The OD scale is logarithmic. Each increase in OD corresponds to a tenfold reduction in transmitted laser energy. For instance, OD 3 reduces laser energy by one thousand times, while OD 6 reduces it by one million times.

Different laser systems require different OD levels depending on their power output and exposure conditions. High-power industrial lasers may require higher optical density ratings than lower-power laboratory systems.

Lens markings usually display both the wavelength range and the optical density rating. This information helps ensure the eyewear matches the laser system being used.

Understanding optical density is an important part of selecting appropriate laser safety eyewear.