What is Transmission? What is Optical Density (OD)?

Transmission with respect to laser protection is a measure of how much energy is passing through a sheet at a specific wavelength. Optical Density is simply a logarithmic scale of that transmission.

OD = -logT(at a given wavelength)

Examples:

OD =0 T=100%

OD=1  T=10%

OD=2  T=1%

OD=3  T=0.1%

OD=4  T=0.01%

OD=5  T=0.001%

So, it is important to observe that an increase in OD by one unit increases protection 10X. When specifying OD, do not assume higher OD means “better”. Higher OD means more dyes and darker sheet which increases cost and decreases user’s vision. It is important to specify the OD you require for your application.