Choosing Eye Protection
The Five Fs of Eyewear
1. Facts -- Specifications of
the Laser and conditions of use.
- Consult your laser's manufacturer's guide for
- Calculate OD and power density requirements based
on wavelength, power in watts (or for pulsed systems,
using wavelength, power in joules, pulse length
in seconds and pulse repetition rate in hertz),
using laser safety software such as Lazan, LaserSafePC,
Easy Haz or the LIA's Laser Hazard Evaluator Software.
- Consider: Are there engineering controls limiting
exposure to the beam? Is partial beam visibility
required for alignment of visible beams? Is protection
required for intra-beam exposure or is protection
primarily for diffuse or scattered energy? For medical
applications, are there different eyewear considerations
for the Clinician and patient (in terms of VLT-visible
light transmittance, full orbital coverage, weight
of eyewear)? Will filter color / color rendition
affect use? Are there multiple laser systems in
the area, or is the eyewear designated for a single
- Consult laser safety eyewear manufacture.
2. Filter -- OD, damage threshold and Visible
Light Transmittance (VLT) requirements.
- Make sure the filter will reduce possible energy
exposure to below the Maximum Permissible Exposure
- Check the Photopic Visible Light Transmittance
(VLT) of the filter. VLT is the percentage of visible
light transmitted through a filter, calculated against
the spectral sensitivity of the eye to daylight.
The higher the better. VLTs below 20% should be
used in well-illuminated working environments.
- Consider Absorptive or Interference filters-Absorptive
filters may be polymer + dye based or glass, and
function by absorbing laser energy. Interference
filters employ thin layers of reflective material
for protection. Hybrids combine both technologies.
- Lightweight polymer filters offer varying VLTs
and mid-level damage thresholds for UV, Visible
and near IR, with lower damage thresholds for IR.
- Polymer filters are cost effective, easy to wear
and offer the highest impact resistance, while heavier
glass filters can offer higher VLTs and higher damage
thresholds at higher expense, and dielectrically
coated and hybrids offer the highest VLTs, highest
damage thresholds (in that some energy is not absorbed
but reflected), at the highest cost.
3. Frame -- Style and mode of wearing.
- Rule #1: if the glasses are uncomfortable, users
will be tempted to not wear them.
- Rule #2: Vanity rules, even in the lab. Users
will wear what they like.
- Many frames are designed to fit-over prescription
glasses. Some are universal, fitting well for those
who do and those who do not wear prescription glasses.
- Ensure that the selected frame is face-forming,
well-fitting with no gaps. Models with sideshields
increase ambient light, cut down on obstructed viewing
and decrease the non-beam hazard of walking into
- Polymer filters are available in the most variety
of frames, often with the widest field of view and
full angular coverage.
4. Fit -- adjustability, comfort, vanity.
- Repeat of Rule #1: If the goggles don't fit, users
won't wear them.
- Repeat of Rule #2: Users won't wear what doesn't
fit well or what they don't like.
5. Factors -- additional considerations.
- Eye protection is only effective when worn-It's
of no use if it's sitting on the shelf.
- If eye protection is too heavy, poorly fitted,
poorly designed or the VLT is too low, users will
make the wrong choice: not to wear it.
- Risk assessment must be part of the equation,
use engineering controls to reduce the risk.
- Filter technical data, including batch data, absorption
characteristics, test reports, CE certificates and
documentation of conformity should be available
upon request or online.
- Consider the source. You only get two eyes.