Protection Against Laser Blindness

Not actually Erin.

Picture by KJ Photography

& is used with permission.

It is becoming increasingly common among certain disruptive groups to use laser pointers as blinding instruments. This is a purpose for which lasers were never designed, but are nevertheless well suited: not only will a laser flash across the eyes dazzle the victim, leaving them temporarily blind and therefore unable to defend themselves, but it can also lead to permanent eye injury and even blindness. 

According to this laser safety factsheet from Iowa University, any laser with an output of at least one milliwatt (1 mW) can cause permanent eye injury. I will not link to it, but it is possible to buy a 300 mW laser online for under $50. Given that many preppers live in the city or other urbanized areas and that unrest in this country is at an all-time high, I believe it would be prudent for some of our readers to take into account the possibility of being struck, either accidentally or deliberately, by a blinding laser. 

Some Science

While lasers come in all colors, green lasers are most commonly used for this purpose due to the human eye's specific sensitivity to that wavelength, likely a genetic heritage from our hunter-gatherer days where being able to differentiate between shades of green helped early humans tell the difference between edible and inedible plants. (Also, the Sun's central wavelength is in the green portion of the spectrum, which likely influences the whole matter.) As such, a green laser will inflict greater damage on our eyes than a red or blue laser of the same milliwattage. 

https://usaphc.amedd.army.mil/PHC%20Resource%20Library/Laser%20Pointer%20FS_24-031-0617.pdf

https://en.wikipedia.org/wiki/Laser_pointer#Colors_and_wavelengths

Eye Protection

Fortunately, it is possible to defend against laser dazzle and eye damage through the use of protective lenses. These lenses will not provide 100% protection against lasers, because lasers are amplified and collimated visible light; any lens which protects 100% against visible light would necessarily be 100% opaque and therefore render you blind by different means. 

Furthermore, effective protection will not come cheaply; if you are not buying certified protective lenses with a known optical density and visible light transmission, you may end up buying colored sunglasses. 

Optical Density (OD) is a measure of un-attenuated laser energy that will pass through a filter. Attenuation is the absorption or scattering effect of the lenses. Therefore the higher the OD, the smaller the amount of high-energy laser light passing through the lens.

Information from https://noirlaser.com/laser-standards

Visible Light Transmission measures how much non-laser light passes through the lenses. While you obviously need light passing through a lens in order to see, this measurement is also useful if you intend to wear protective lenses at night, when you will need a higher VLT than during the day. 

Information from https://www.opticnerve.com/pages/visible-light-transmission-vlt

Armed with this knowledge, let's take a look at a certified pair of protective laser strike glasses, the Model 33 from Phillips Safety Products.

Optical Density:

• Over 7 for wavelengths between 190nm and 400nm, which means it highly attenuates the ultraviolet spectrum. 
• Violet pointers emit between 405nm and 445nm, for which the OD starts at 7 but rapidly drops off to 2 (reducing laser dazzle by 99%). 
• Blue pointers emit from 450-488nm, so OD against blue is 2 to perhaps 0.5, reducing dazzle from anywhere between 90% and 50%. 
• Green pointers emit between 515 and 532 nm, and these glasses are rated over OD 2 for that, reducing dazzle by 99%. 
• OD zero for anything in the yellow, orange, red, or infrared spectrum. 

Visible Light Transmission: 33%, meaning that these have a tint equal to regular sunglasses. 

Conclusion: Good protection against violet and green lasers; adequate to poor against blue; no protection against red lasers. I base this conclusion on the fact that 99% attenuation against a 300mW green laser still leaves 3mW of laser energy reaching your eyes, which can still cause injury. 

An OD 3 would be preferable, as that would reduce the laser energy to 0.3 mW, well below the threshold of injury. Unfortunately, I cannot find any certified lenses of OD 3; for example, these glasses have an OD 4 and VLT of 55%, but the low price and lack of visible certification made me think they were too good to be true. A quick chat with their online customer service confirmed it. 

If you happen to come across any certified OD 3 glasses in the 520-532nm range, preferably with a VLT of 50% or more, please let me know so that I can buy them. Until then, I guess I'll have to spend $150 for OD 2. That's expensive, I know, but my vision (and potentially my life) is worth that much.