The correct spark plug and gap is crucial to proper ignition. Spark discharge is a breakdown in the air insulator between the electrode and ground. Yes - air is an insulator, a pretty good one at that. As voltage builds at the electrode, atoms in the air within the air gap gain electrons. This process is called ionization.
It's one of the reasons why our standard lenses are polycarbonate (thinner than standard lenses typically sold by other eyeglasses retailers). At Warby Parker, you can upgrade to high index lenses for an additional $30 whereas it typically costs $60 to $100 more.
Best Answer: at walmart lens start at $70 (plastic with no coatings(i would get coatings they are about $40 more)) poly lens are $110-$140 and high index lens are $160.. Well, it depends on the location. For us, lenses start at $84 for plastic, single-vision lenses. A polycarbonate lense is $25.00 more. It's a shatter-resistant, scratch-resistant lense. Bifocals start at $94.00 for plastic and again, you add $25.00 for poly.