The latest gizmo to be adopted by top-secret special forces troops fighting the Wars on Stuff is liquid crystal ballistic sunglasses which can change colour automatically much faster than traditional "photochromic" offerings - or at the touch of a button.
The US Office of Naval Research says it designed the new Fast-Tint Protective Eyewear (FTPE) lenses to the requirements of the famous yet reclusive US Navy SEAL frogman-commandos. In common with other Western troops nowadays, the SEALs are encouraged more and more to wear protective eyewear in combat - potentially saving their sight from damage by flying fragments, grit, stones, blast etc.
As with the other troops, the SEALs have been issued a range of different-coloured interchangeable lenses for different light conditions. But this is too fiddly for situations such as assaulting buildings where operators will move swiftly from blazing outdoor sunlight to dark or dim interiors. SEALs on such an operation tend to simply take their sunglasses off as they go through the door - just before the guns and grenades start going off and the air fills with flying bits and pieces.
A possible solution might be so-called "photochromic" lenses (phototropic would seem more like the right word), well known under brand names such as Reactolite. But these take too long to change tint, and also they actually react to ultraviolet rather than visible light - which means that they won't necessarily darken in response to heavy sunlight through a window (as the UV doesn't penetrate the glass). Nor is there any way to manually select a particular tint or colour.
Hence the FTPE lenses, which are effectively basic liquid-crystal display screens. They can turn amber, blue, grey or clear when a small electric charge is applied - either by a miniature light-sensing automatic unit, or at the touch of a button.
"Transition time is less than 0.5 seconds," says the ONR's Stephanie Everett.
According to an ONR statement, 30 sets of FTPE goggles and glasses are at war with the SEALs right now, and 100 more have been ordered based on performance so far.
"We expect additional minor design changes based on the results of the current assessment," Everett says.
As has occurred with other items of kit (bomber jackets, cargo trousers etc), the civilian sunglasses market was originally almost created by military sunglasses - specifically the aviator specs of the 1940s - and there's always a chance that instant-colour-change tech might be the next must-have thing. One does note that Ohio firm AlphaMicron, credited by the ONR for developing the new SEAL-shades alongside navy boffins, already has "E-Tint" motorbike visors, ski goggles and auto-dimming vehicle mirrors on offer. ®
Readers will of course have noted that the FTPE/E-Tint lenses could be controlled by various other types of sensor or device than simple light-meters or manual buttons. It would seem entirely possible to produce a version which responded to bio-telemetry from the wearer, for instance, allowing the specs to become opaque in the event of any nervousness: or still more sophisticated kit might detect actual threats and adjust lens tint accordingly.
Thus a near-analogue of the famous Joo Janta Peril Sensitive Sunglasses worn by Zaphod Beeblebrox in the Hitchhikers' Guide to the Galaxy saga would seem at last to be within our grasp.