Essentially, a low VLT% lens will transmit less light and will be dark to look through, whereas a high VLT% will transmit more light, and will be lighter to look through.

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In the image above, you can see a visual scene as perceived while wearing no LEP (left column), an OD 1 LEP (middle column), and an OD 3 LEP filter (right column), when exposed to no laser (top row), a lasser irradiance of ≈ 5mW laser pointer (middle row), and a laser irradiance of ≈ 500mW (bottom row)

LEP lenses are inherently tinted/colored due to the reduced light transmission and wavelength-blocking characteristics, which changes the way any given color is perceived. In turn, this challenges color discrimination and visual detection. Additionally, a high OD often results in an increased color distortion of the image. That is why it is vital to assess the threats and hazards, which is needed to be protected against in order to identify the lowest OD possible to mitigate the visual impacts.

Similarly, the Civil Aviation Authority reported 775 laser illuminations against UK commercial aircraft in 2018¹, while the Federal Aviation Authority reported 6.852 incidents against U.S. commercial aircraft in 2020².The same accessibility to lasers has also elevated the use of both visible lasers (red and green) and invisible lasers (Near Infrared (NIR)), as target pointers and laser target designators in militaries worldwide. However, this enhanced use has also increased the risks of soldiers, unintentionally, being exposed to harmful lasers, the risk being even higher with NIR lasers since they are, by nature, invisible.

As demonstrated in the table below, lasers come in many different power outputs. An off the shelf laser presentation remote is, usually, a class 2 laser below 1 mW, which does, as such, not pose a big threat.  Nevertheless, it is possible to acquire very powerful laser pointers online, which are in class 4. Most military and law enforcement target pointers for weapons are class 3R – a few being class 3B – and most laser target designators are class 4.

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Visible Light Transmission (VLT):Depending on the tint of the eyewear, light, to a higher or lesser degree, is allowed to be transmitted through the lens. This is often expressed in percentage of luminous transmittance of visible light through the lens. This is measured using a photometer and graded accordingly.

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Scotopic Vision is the vision of the eye under low light conditions (night adjusted eye). Cone cells do not function as well as rod cells in low level lighting, so scotopic visions happen completely through rod cells. Photopic sensitivities are at a maximum in green light at about 555 Nm, which is the wavelength at which the cones in our retina are most receptive. However scotopic sensitivities peak about 50 Nm lower in the blue-green region of the spectrum at 507 nm, where the rods are most receptive.

Integrated Visual Photopic Transmission (IVPT).This calculation is weighted by the spectral response of the day-adapted human eye to approximate the human perception of transmission through a filter.

Frequency:Nanometers (Nm) define which type/color of laser (wavelength), which the lens will protect against. For instance, 532 Nm is the predominant of green lasers.

When discussing laser eye protection, used day and night and against visible and NIR lasers, it is important to add a few more aspects than the above VLT, which only covers the day adapted eye and the visible spectrum of light.

The scotopic value is very important, especially when it comes to lenses that should be used during low light or nighttime operations. As described and illustrated above, the scotopic value indicates the visibility in very low light (night adjusted eye). If the scotopic transmission of a laser lens – or any lens for that matter – is too low (app. below 15%), the result would be like using a classic regular grey lens at night. The use of it will be very limited, as the rods capabilities to function will be significantly decreased.

The selected Nm in combination with the level of OD affects the VLT. The more different Nm there is combined in a lens, the lower the VLT will become. The same goes for the OD. The higher the OD, the darker the lens. So, if you want to create “the perfect laser protection lens”, protecting against all Nm, the lens will become very dark – close to useless. Therefore, it is important to do a proper risk and hazard assessment to select the lens combination you need.

Integrated Visual Scotopic Transmission (IVST).This calculation is weighted by the spectral response of the night-adapted human eye to approximate the human perception of transmission through a filter.

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To visualize this distortion and the effect of two different lasers on two levels of OD, the images below illustrate, how LEP affects vision in terms of coloration, transmission, and dazzle suppression.

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To address the military personnel and law enforcement’s need for a defense against flash blinding – the tactic of using lasers to obstruct the vision, which can cause disorientation, optical distortion, and long-term eye damage – we have created our ballistically-rated laser eye protection lenses. These lenses are infused with protective dyes to refract various laser wavelengths, and, in this way, protect the eyes of the military personnel and law enforcement officers.

Photopic vision is the vision of the eye under well-lit conditions, normally usual daylight intensity. It allows color perception, which is mediated by cone cells. Cone cells have a higher visual acuity, as well as providing the eyes’ color sensitivity.

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Optical Density and Distortion:The Optical Density (OD) defines the level of protection against the given Nm. For example, if a laser pointer has a safety distance to the naked eye at 100 meters, you are safe at 10 meters, when wearing laser eyewear protection with an OD of 1. With an OD of 2, you are safe at 1 meter etc.

Through the last decade, Police and Homeland Security Forces worldwide have seen an increase in the threat from malicious use of laser pointers, as the inexpensive gadgets have become more accessible and high-powered. Protesters have found a particular liking to the green lasers, as the proportionate distribution of laser colors at protest are as following:

Having the complexity of the technology in mind, Wiley X have put different standard combinations of laser protection lenses together. Combined, the setups cover the full spectrum of the main Nm used in the branches of military and law enforcement.

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As demonstrated in the table below, when wearing an OD 5 LEP lens, a laser with a laser safety distance of 2 kilometers will now be safe to view at a distance of 2cm.

Laser protection technology provides multiple solutions to achieve the necessary protection. There are three main elements that needs to be considered: