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Missed Boy Scouts? No Problem. Learn How To Use Your Glasses To Start A Fire

By Essilor News

Starting a fire with your glasses is one of those weird science tricks everyone has heard of, but never actually tried. After all, that's what we have matches and lighters for, right? And unless your three hour cruise ends with you washed up on the shore of an uncharted desert isle, chances are you'll never need to make fire with your glasses.

But can it actually be done?

Here's a look at the facts and myths as we explore just how you can start a fire with your glasses.

The Science: To understand why starting fires with your glasses works, first we have to understand how the lenses in your glasses correct your eyesight.

When light enters your eye, it is focused into an image on your retina. Sometimes, due to various issues with your eye, the focal point will be in front of the retina (which causes nearsightedness) or behind the retina (which causes farsightedness). The lenses in your prescription eyeglasses correct these problems by bending the light before it hits your eye in order to compensate, one way or the other, for your vision problems.

It's this bending of the light that allows you to start a fire with your glasses - depending, that is, on what type of glasses you have.

The Glasses: There are two main types of corrective lenses: Converging lenses and diverging lenses. Diverging lenses, which are used to correct nearsightedness, bend the light further away from the focal point, while converging lenses, which correct farsightedness, bend the light towards the focal point.

As a result, if you are nearsighted, your glasses won't help you start a fire, because they are actually dispersing the light instead of focusing it.

If you are farsighted, however, you are in luck, because your glasses will bend the light inward towards a focal point. And it's this focal point that will allow you to create fire.

Though, ironically, you may need some water to do it.

The Water: Starting fire with your glasses is essentially the same as starting a fire in your back yard with a magnifying glass when you were a little kid. But there's one major difference: Magnifying glasses are biconvex.

That's a fancy way of saying that the lens of a magnifying glass is curved in both directions, as opposed to your glasses, which are only curved in one direction. Being biconvex means that a magnifying glass bends the light twice, once when it enters the lens and again when it leaves. This produces a more focused beam of light, which in turn creates more heat and makes it easier to start a fire.

Most glasses aren't powerful enough on their own to create fire, as the light isn't focused quite enough. But there's a simple solution: A drop of water on the inside of the lens. Placed in the middle of the lens, this drop of water will also bend the light, turning your glasses biconvex - and allowing you to start a fire.

The Fire: Now the fun part. After preparing your target - tinder, kindling or other suitable material for a fire - hold your glasses up between the sun and the target. The light will appear as a small circle or dot. Your goal is to find the proper height and angle for your glasses to make this circle of light as small and as focused - perfectly round is best - as you can.

If it's a sunny day and you're working with dry tinder, you should start to see smoke within 20-30 seconds. Congratulations! You've just made fire with your glasses.