1. What is Optical Density (OD)?
Optical Density (OD) is a logarithmic measure of transmittance defined by the Beer-Lambert relationship:
OD = -log10(T) = log10(P_incident / P_transmitted)
For example, an OD of 6 at 1064 nm reduces transmitted power by a factor of 1,000,000 (10^6). While OD defines optical absorption at low or non-destructive power levels, it does not evaluate whether the filter material will physically melt, crack, or bleach when struck by high-energy industrial or medical laser beams.
2. What is an EN 207 LB Rating?
The European EN 207 standard evaluates the complete product under real laser fire. To receive an LB rating (from LB1 to LB10), the filter and frame must satisfy two requirements simultaneously:
- Deliver the required optical density:
T(λ) ≤ 10^(-LB) - Withstand direct laser beam impact (5 seconds for CW or 50 pulses) without undergoing physical breakdown or degradation.
3. The Danger of Relying Solely on OD
In high-power laser applications (e.g., fiber laser cutting, surgical lasers), polycarbonate goggles with OD 7 might burn through or discolor in less than a second if not reinforced for laser power density. In European jurisdictions and international best practice, EN 207 certified protection is mandatory for Class 3B and Class 4 equipment.