Optical density (OD) is a measure of how much laser radiation is absorbed or blocked by a protective lens. Because the scale is logarithmic, each OD level reduces transmitted energy by a factor of ten. This means OD 5 reduces exposure by 100,000 times, while OD 6 reduces it by one million times.

The required OD depends on the laser’s power, beam characteristics, and the potential for exposure. In environments where high-power lasers are used, higher OD ratings are typically necessary to ensure adequate protection.

One important consideration is visibility. As OD increases, visible light transmission may decrease, which can affect brightness and colour perception. Selecting eyewear that provides the required protection without excessively limiting visibility can improve comfort and usability.

Lens markings often include OD ratings along with wavelength ranges and performance classifications. Learning how to read these markings helps users confirm that protective eyewear is appropriate for their equipment and working conditions.