Military eyewear is designed with ballistic rated polycarbonate lens for tactical and combat environments to handle the extreme conditions and impact hazards. The specifications far exceed normal industrial safety standards. The important features to look for in a Military Eyewear are
- Lens Material
- UV 400 Protection
- Anti Scratch Coating
- Anti Fog Coating
- Polarised Lens
- Ballistic Lens
Out of all the material available, polycarbonate is the best lens material for tactical goggles since it scores on three important aspects of lens properties - Impact resistance, weight and inbuilt UV protection. Polycarbonate has the best impact resistance and is suited for making ballistic goggles. It is virtually unbreakable and doesn’t shatter even at high impact. It weighs less than half the weight of glass resulting in an eyewear that is lighter and more comfortable to wear. It blocks 100% of UV rays and doesn’t require any special UV blocking lens coating. They are also cheaper than Trivex lenses. The drawback of polycarbonate is that it is softer than glass and more susceptible to scratches even with an anti scratch coating.
UV 400 Protection
Ultra Violet rays are electromagnetic radiation coming from the sun which cannot be seen. Long term exposure to UV rays will result in serious eye damage. UVA, UVB and UVC are the three types of UV rays of which UVA is the most damaging to the eyes followed by UVB. Most UVC is blocked by the ozone layer. Polycarbonate and Trivex lenses have inbuilt UV blocking properties and blocks 100% of UV and HEV up to 400nm (UV400 protection).
Related Test Standards
EN 170 tests the protection of the object against ultraviolet radiation.
Anti Scratch Coating
Anti-scratch coating is a thin transparent protective coating applied on the lens surface to prevent hairline scratches that easily happens on all kinds of lens thereby increasing the durability of the glasses without interfering with the way the lens functions. Polycarbonate lenses are much softer than glass lenses and are more susceptible to scratches when being cleaned or accidental fall on the ground. Lenses with anti scratch coating are resistant to scratches but, are not scratchproof. This coating is applied by spraying, dipping or manual application based on the surface to be coated. In tactical eyewear, the anti scratch coating is usually applied on the outer surface and on the inside, anti fog coating is applied to prevent fogging in cold weather. It must be noted that only one type of coating can be applied on any lens surface. Eyewear with lens having the same type of coating on both surfaces are cheaper since it involves the simple process of dipping the lens in the solution whereas eyewear with lens with different kinds of coating on the two surfaces are much expensive since it involves the laborious process of applying the coating on each surface separately. To prevent scratches, it is necessary to store the glasses in the soft case provided and clean the lens surface using the soft microfiber cloth supplied with the goggles. Extra care has to be taken while cleaning the inside surface since it is usually coated with anti fog coating instead of anti scratch coating.
Anti Fog Coating
In cold weather, fogging appears on the inner surface of the lens when they are significantly cooler than the outside temperature. This is not just annoying but also a safety hazard since it limits your vision and in extreme cases dangerous for military and law enforcement personnel. Anti fog coating is the most important feature in a military goggles. The goggle is of no use in combat zone if it has to be taken off due to fogging. This problem is also prevalent in eyewear used by sportsmen when their body temperature is hot and perspiring. To mitigate fogging when one moves from a cooler area to a relatively warm area, a transparent anti fog coating is applied on the inside surface of the lens. This coating reduces the dew point and thereby delays condensation of water droplets on the lens surface. This coating is applied to the inside surface of the lens and they can be applied on all kinds of lenses like polycarbonate, plastic and glass. A simple way to test if your glasses have anti fog property is to hold the lens surface against the steam rising from a glass filled with hot water. If the lens has an anti fog coating then, there won’t be any fogging on the lens but, without the coating the water droplets will start condensing in a few seconds. Fogging cannot be eliminated but, can only be delayed. There is no fog proof goggles. At the right temperature and humidity even the anti fog coated lens will fog. The challenge is to prevent the humidity build up inside the goggles and this can be achieved by air circulation which will exchange the humid air inside the goggle with the less humid air outside.
Related Standards- EN168
Polarised lens are a kind of lens which reduces glare from surfaces such as snow, water, glass, road and other shiny surfaces by cutting off the horizontally polarized rays reflected from these surfaces. When sunlight falls on reflective surfaces it bounces off and gets polarized mostly in a horizontal plane. Therefore the polarized lenses are polarized vertically thus drastically reducing the horizontal glare. Glare is a bundle of concentrated polarised light which is produced after light hits a horizontal reflective surface. The polarization is not always horizontal and can be in any direction but, since most reflective surfaces like water and road are horizontal, polarization mostly occurs in the horizontal plane. Polarised glasses filter out these undesirable reflected light and provides a clear view.
Advantages of Polarised Lens
They are very popular among fishermen and photographers since it cuts the reflected light for the water surface and the wearer is able to see clearly below the surface of water. They increase visual clarity, contrast and acuity and can be easy on the eye during long drives on a sunny day. It is the ideal eyewear for people who are sensitive to light.
Disadvantages of Polarised Lens
Polarised lenses come in a maximum thickness of 1.2 mm and this result in low impact resistance which means that they are not the best lens for ballistic eyewear compared to non polarized lenses which are thicker. When LCD screens like mobiles and watches are seen through polarized glasses, at certain angles it is difficult to see the screen or the display may completely disappear. It is not recommended for pilots who rely on LCD instrument panel as they might find it difficult to read their instruments and viewing objects in the sky. They should not be used at night or in low light conditions as it reduces the amount of light entering the eyes.
Ballistic eye wear protects the wearer from small projectiles and fragments. Military grade polycarbonate lens are used in the making of these lens.
There are three standards used to test Ballistic Eyewear
- US Civilian Standard - ANSI Z87
- US Military Standard - MIL-PRF-32432
- European Standard - EN166
US Civilian Standard - ANSI Z87
ANSI-Z87- Practice for Occupational and Educational Eye and Face Protection. ANSI stands for American National Standards Institute. It tests with projectiles traveling at 150 FPS. ANSI certified eye wear are good for civilian or industrial use. They are NOT recommended for military use.
US Military Standard - MIL-PRF-32432
MIL-PRF-32432 Military Combat Eye Protection Standard (MCEPS).
The speed used for MIL standard is four times the speed used for ANSI testing. Glasses (MIL-PRF-31013) and goggles (MIL-DTL-43511D) are tested differently. Testing of glasses requires a 0.15 caliber, 5.8 Grain, T37 shaped projectile impact at 640-660 feet per second while goggles require a 0.22 caliber, 17 Grain, T37 shaped projectile impact at 550-560 feet per second
European Standard - EN 166
EN 166 is an European norm which defines the basic requirements of personal eye protection. It is closely related to EN 167 and EN 168 which specify the optical and non-optical test methods respectively.
EN 167 (Optical tests) defines the optical requirements for the protective eyewear: spherical, astigmatic and prismatic power.
EN 168 (Non Optical tests) determines non-optic tests like the test on increased robustness, stability at elevated temperatures, UV resistance and resistance to ignition, high speed impact, resistance to fogging and protection against gases, dust, and smoke.
Detailed information of EN standards related to ballistic goggles can be found here https://www.wiseworksafe.com/blog/view/understanding-en-166-personal-eye-protection-standard
Difference between Goggles, Sunglasses and Eye Shields
Goggles, Sunglasses and Eye Shields are all designed in different ways to serve different purposes but, the usage overlaps in some cases. People often use these terms interchangeably to refer to all kinds of eyewear while in actual, these terms refer to a specific type of eyewear. The basic difference between goggles and sunglasses/eye shields lies in the usage, where goggles protect you from physical particles or objects in addition to sunlight, while sunglasses are designed primarily to protect you from harmful sun rays.
Goggles are designed with side shields and elastic bands to fit snugly around the eyes without any air gap, to protect you from dust, wind, snow, debris and other objects. The protection it provides also varies based on the application for which it is designed. A tactical goggle is designed to protect soldiers from secondary splinters in combat zone and the components that go into its making are superior compared to a protective goggles that is used in laboratories to protect the eyes from chemicals or sports goggles, like the ones used by swimmers, which are used to prevent water from entering the eyes. Some bigger goggles are designed for use over the glasses which are worn over the prescription spectacles. Goggles are used for specific operations while sunglasses and eye shields are for every day use.
Sunglasses and Eye shields are designed to protect the eyes from glare and UV rays. The term sunglasses refers to an eyewear with a frame that goes all around the lens while in an eye shield the lens are attached to the frame only at the top. They are light weight and less bulky compared to goggles and is suitable for long hours of usage. Sunglasses and eye shields are used as a fashion trend. The lens can also be replaced with prescription lens. They are much cheaper compared to goggles.