Choosing the Right Protective Filters for Your Application

Laser safety within the operating environment should be paramount in importance. The nature of laser light can have profound effects on human tissues should an inadvertent exposure occurs. This article describes general safety tips for protection against eye exposure and how to locate appropriate eye protection filters on our website.

Finding An Appropriate Filter

Few protective eye filters attenuate only single wavelengths. Most attenuate several wavelengths or a broader range around a single wavelength. As such, there can be significant overlap between categories of protective glasses. This can make finding the best filter for your application time consuming and difficult. The OEMLaserSystems.com website reduces this burden by providing search capabilities for specific wavelengths or types of laser systems.

Filter Search

Click on the PRODUCT SEARCH link at the top of the page. Enter the search term 532nm goggles and press enter. Our wavelengths are indexed in nanometers (nm) so always include nm right after the wavelength you enter with no spaces. Follow the wavelength with the term goggles, glasses, or spectacles. This will filter out all the laser systems leaving the search results displaying only the protective eye wear. In the case of 532nm goggles, about two dozen filters are displayed. The descriptions of the filters in the list can be used to narrow down the selection. For example, if the filter is not required to protect against 808nm or YAG, these can be disregarded. Any wavelength can be entered. Our search function, however, only contains several hundred of the most common wavelengths. If a search returns no results you may have to select a more common wavelength near the wavelength of your system and verify its usefulness with the specified ANSI or CE ratings.

You can enter multiple wavelengths in the search field to narrow down filters that protect against two or more wavelengths. Enter the term 473nm 532nm goggles, as an example, and the results return several filters that are protective against both wavelengths. A rule of thumb to bear in mind is the more wavelengths entered the less the probability of a match. The search page also describes the use of logical operators such as AND and OR and the use of quotation marks and parentheses to assist in narrowing down particular products. Also keep in mind, if you having difficulty locating a filter for your application, please contact us. We are happy to assist you.

Once you have your filter choices, there are a few additional things to consider.

Visible light transmission (VLT)

Visible light transmission is the portion of ambient light and filtered light that passes through the filter. The VLT is indicated in the specifications table of every filter we offer. Too dark of a lens may become as much of a safety hazard as viewing the laser without filters. This is due to the fact that users will often remove or lift their filters to see their work rendering the user unprotected. Filters with a VLT below 20% should be used in brightly illuminated areas.

Laser Wavelength

It’s very important that your protective eye wear protects against the wavelength with which you are working. Be sure to switch filters when switching lasers, unless of course the filters are appropriate for both wavelengths. If the laser is UV or infrared additional cautions must be observed. The beam is invisible, but may still blind you. Always verify the protective capability of the filter against the wavelength and power of the laser in use. All ratings are etched onto the filters for easy verification.

Z136 Ratings

The OD rating of the goggle is the log10 attenuation of the laser light.

Optical Density (OD) Scale

Optical Density (OD) Transmission in % Attenuation Factor
0 100% 1
1 10% 10
2 1% 100
3 0.1% 1,000
4 0.01% 10,000
5 0.001% 100,000
6 0.0001% 1,000,000
7 0.00001% 10,000,000

EN207 Ratings

The EN207 European standard is more definitive than Z136 standards. It breaks down the exposure by time periods and by wavelength. The time periods are listed as D, I, R, and M and are described below.

D - Continuous Wave
I - Pulsed Mode (>1µs - 0.25s)
R - Giant Pulsed Mode (1ns - µs)
M - Mode Locked (<1ns)

The chart below describes what minimum rating is required for a particular power or energy density based on the wavelength and operational status of the laser. For example, a 1064nm q-switched laser with a 10ns pulse with a power density of 103 J/m2 would require at least an L5 filter.

European Laser Safety Regulations

Scale

Number

Maximum Spectral

Transmittance for

Laser Wavelength

Maximum Power (E) and Energy Density (H) in the Wavelength Range

180nm - 315nm >315nm - 1400nm >1400nm - 1000 microns

D
W/m2

I, R
J/m2

M
W/m2

D
W/m2

I, R
J/m2

M
J/m2

D
W/m2

I, R
J/m2

M
W/m2

L1 10-1 10-2 3x102 3x1011 102 5x10-2 1.5x10-3 104 103 1012
L2 10-2 10-1 3x103 3x1012 103 5x10-1 1.5x10-2 105 104 1013
L3 10-3 1 3x104 3x1013 104 5 0.15 106 105 1014
L4 10-4 10 3x105 3x1014 105 50 1.5 107 106 1015
L5 10-5 102 3x106 3x1015 106 5x102 15 108 107 1016
L6 10-6 103 3x107 3x1016 107 5x103 1.5x102 109 108 1017
L7 10-7 104 3x108 3x1017 108 5x104 1.5x103 1010 109 1018
L8 10-8 105 3x109 3x1018 109 5x105 1.5x104 1011 1010 1019
L9 10-9 106 3x1010 3x1019 1010 5x106 1.5x105 1012 1011 1020
L10 10-10 107 3x1011 3x1020 1011 5x107 1.5x106 1013 1012 1021

 

Bear in mind the charts above are only a starting point. Always have your local laser safety officer determine the appropriate filter as the LSO considers not only the raw calculations but also the operating environment such as the nominal hazard zone (NHZ), the experimental setup and a host of other factors that may increase or even decrease the required rating of the filter.

If you have any questions regarding our protective filters please send us an email or give us a call.

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