It'a about motorcycle windshields.
Once or twice a year, we'll get a call from an upset customer claiming our windshield melted the dash or instrument panel of his/her motorcycle.
To be fair, our competitors get those complaints also, as do the OEM manufacturers. Why does this happen?
THE ANGLE OF INCIDENCE EQUALS THE ANGLE OF REFRACTION
Remember that from science class? Or from trigonometry?
I didn't, either. That's what happens when you fall asleep. You miss stuff.
But to get to the heart of this discussion, recall a certain experiment in refraction from your youth...
...and you'll start to guess how and why motorcycle windshields can melt plastic instrument panels.
IT GETS A LITTLE MORE COMPLEX
Your typical touring or sport-touring motorcycle windshield is designed with a curved, three-dimensional form, both on the horizontal axis and the vertical axis. This makes it more effective in managing wind and turbulence while blasting down the highway at 80mph.
It also makes it more effective in concentrating light waves and heat energy -- both refracted and reflected -- when the motorcycle is parked in direct sunlight.
You can read here and here to learn about the refractive index of transparent substances such as glass or plastic. But just keep in mind that, unlike a comparitively flat automotive windshield or a vertically flat cruiser windshield, your sport/touring windshield has a complex convex/concave curvature that can bend and concentrate the sun's light/heat waves with surprising and unexpected efficiency. In addition, your dark black dash panel loves to absorb and store radiated heat energy.
Note: UV coatings, like those we apply to our own windshields, do not materially alter the physics of refracted light — they merely block the absorption of ultraviolet radiation in order to limit the long-term molecular degradation of the plastic. Our UV coating, for example, has a 10-year lifespan rating.
SO WHAT DO YOU DO?
It's simple. If you want to keep your instrument panel from melting, park your bike in the shade. If that's not possible, park at a 90-degree perpendicular angle to the sun's path. Generally, point your wheels either north or south.
DO NOT park your bike directly facing the sun (0-degree) or directly opposite the sun (180-degree). Your bike should cast a shadow on either the left or right side.
Sometimes you may not have a choice, so cover your bike's dash panel with some opaque material, like your jacket.
And remember, while you're enjoying a cool refreshing beverage in a comfy air-conditioned tavern, your motorcycle is out there sweating under a blazing hot sun.
Be nice to your bike and treat it kindly.
Or else the flying monkeys will come after you.