Final laser safety product selection should always be reviewed by the on-site Laser Safety Officer (LSO) or other qualified laser safety personnel based on the actual laser system, operating conditions, beam characteristics, and applicable ANSI standards.
Optical Density (OD) in laser safety describes how much laser radiation at a specific wavelength is attenuated by a protective filter or material. OD requirements used in the United States are primarily based on the ANSI Z136 series of laser safety standards, which consider several factors including laser wavelength, exposure duration, beam characteristics, and biological impact to the eye and skin.
Different wavelengths interact with biological tissue differently, which is why laser safety protection must always be selected based on the specific laser wavelength being used.
Below is an example of how to read optical density shorthand notation and understand the attenuation provided by a given laser safety filter.
How to Read Optical Density (OD) Specifications
Optical Density is always tied to a wavelength or wavelength range.
For simplicity, OD values are typically listed across a wavelength range rather than for every individual wavelength.
Below is an example for how to read the shorthand notation for optical density and the attenuation of energy passing through a given filter.
Another example:
OD 7+ @ 190–385 nm
This means the filter provides a minimum Optical Density of 7 across the wavelength range of 190 nm through 385 nm.
Higher OD values indicate greater attenuation of laser radiation.
Wavelength is the first parameter needed when assessing the type of laser safety protection required.
Optical Density Is Wavelength-Specific
Optical Density values only apply to the wavelengths specifically listed for the laser safety product.
Protection should never be assumed outside the stated wavelength range.
For example:
A filter rated OD 7+ @ 190–385 nm should not automatically be assumed to provide protection at 110 nm or 450 nm unless those wavelengths are specifically listed.
Laser safety products are engineered and tested for specific wavelength ranges, and proper protection selection should always be based on the actual laser wavelength being used.
Why Wavelength Matters in Laser Safety
Many lasers operate at completely different wavelengths, and different wavelengths interact with the eye and skin differently.
Laser safety standards account for these biological differences when determining required protection levels.
Laser radiation may fall into several general regions of the electromagnetic spectrum:
Ultraviolet (UV)
Visible light
Infrared (IR)
Visible light generally ranges from approximately 380 nm (violet) to 740 nm (red).
However, many industrial, medical, scientific, and military lasers operate outside the visible spectrum in ultraviolet or infrared wavelengths, requiring specialized laser safety protection.
Knowing the exact wavelength of the laser system is critical when selecting appropriate PPE.
Operating Beam vs Aiming Beam Lasers
Many laser systems utilize both:
An operating beam
A lower-powered aiming beam
The aiming beam is typically used to assist the user in positioning or aligning the operating beam.
In many systems, the aiming beam is low powered and often visible red light. However, users should never assume an aiming beam is automatically eye-safe.
The operating beam is the beam which performs the actual cutting, welding, marking, engraving, medical treatment, or scientific process and typically requires full laser safety protection.
Operating Beam Laser vs Aiming Beam Laser (Typically Eye-Safe)
A common example of an aiming beam is a laser pointer used for positioning or alignment.
If you are uncertain whether an aiming beam is safe for diffused viewing, consult your Laser Safety Officer (LSO) or contact us before making assumptions. Our team has encountered systems where the aiming beam itself required laser safety protection.
Never intentionally stare directly into any laser beam, including aiming beams.
For more information on laser safety with an operating beam vs an aiming beam, see here.
Laser Alignment and Aiming Beam Safety
Laser alignment procedures require additional caution.
If the alignment beam exceeds the Maximum Permissible Exposure (MPE), proper laser alignment eyewear should be used where appropriate exposure limits are maintained.
At the same time, excessive attenuation during alignment can create visibility issues, making alignment itself more hazardous.
Proper laser alignment procedures typically involve:
Appropriate alignment eyewear
Standard operating procedures (SOPs)
Trained personnel
Controlled beam paths
Proper positioning during alignment
Personnel should remain behind the beam path whenever possible and avoid placing their eyes near the beam axis during alignment procedures.
All laser safety PPE is intended for unintentional direct and diffuse exposure scenarios only.
If accidental eye exposure occurs, immediately look away from the beam and seek appropriate medical evaluation if necessary.
Why Higher Optical Density Is Not Always Better
A common misconception is that higher OD values are always preferable.
In reality, excessively high OD values can:
Reduce visibility
Make alignment procedures more difficult
Reduce situational awareness
Increase operational difficulty
Proper laser safety involves balancing protection with the ability to safely perform the task.
For example, laser alignment eyewear often intentionally allows limited beam visibility so alignment can be performed safely without completely obscuring the beam.
Laser safety protection should always be selected based on:
Laser wavelength
Laser power or energy
Exposure duration
Beam geometry
Operational environment
Applicable ANSI standards
Common Questions About Optical Density (OD)
If my glasses have an Optical Density of 7+ between 190–385 nm, does that mean they also protect at wavelengths below 190 nm, such as 110 nm?
No.
Laser safety protection should never be assumed outside the specified wavelength range for the product.
Protection must always be selected based on the actual wavelength of the laser system being used.
Why do some laser safety glasses list multiple wavelength ranges and overlapping OD values?
Many laser safety products are designed to protect against multiple laser wavelengths or multiple laser types.
Because filter performance changes across the spectrum, manufacturers often list several wavelength ranges with different Optical Density (OD) values.
For example:
OD 7+ @ 190–385 nm
OD 5+ @ 800–1100 nm
OD 7+ @ 1064 nm
In this example, the filter provides different levels of attenuation at different parts of the spectrum.
Sometimes a smaller wavelength range may appear inside a larger wavelength range because the filter provides increased protection at a particularly important wavelength.
This is common for lasers such as:
Nd:YAG (1064 nm)
Fiber lasers (1030–1080 nm)
Alexandrite lasers (755 nm)
Laser safety filters are not uniform across all wavelengths, which is why wavelength-specific OD values are listed separately.
Can one pair of laser safety glasses protect against every laser?
No.
Blocking the entire visible light spectrum would severely reduce or eliminate visibility, defeating the purpose of wearing protective eyewear.
However, many laser safety products are designed to protect against multiple wavelengths or multiple laser systems.
In some applications involving multiple unrelated laser wavelengths, users may require different eyewear configurations or additional engineering controls.