These lens covers aren't just hi-vis, they're Hyper-Vis.  Working with optical engineers and academic researchers, they've created a proprietary color not originally found in nature.  This isn't just another yellow lens, this is a highly specialized tint of yellow not in any flora or fauna.  As our brain is not accustomed to seeing this specific color, it really stands out against our natural color palette. 

Another added benefit to the yellow/amber color family is its ability to penetrate dust.  Similar to the colors found at the particle level in dust, the light does not reflect back and is mostly absorbed; you can see better in dusty conditions as compared with a standard white light.

Finally, another layer of protection between flying rocks and debris to protect your housing.  The 100% silicone bezel ring make installation and removal simple and effective.  The inside of the ring is a grippy silicone that sticks, simply slip it on, no tools required.

Sold as a Single unit.