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How to Start a Fire with Glasses

Backpacker with sunglasses on a bright, sunny day
Backpacker with sunglasses on a bright, sunny day

“Now make that dot as small as you can make it,” I coached my son Carter in the backyard, “Keep it nice and still.”

Holding a fresnel lens, Carter watched intently as the small glowing dot began to heat the center of a dry leaf.

“It’s smoking!”

A few moments later the small pile of leaves burst into flames and Carter had started his first fire using the magnified power of the sun. If you have never played with the sun’s magnified rays, then it can seem like magic when someone bends down and uses their own eyeglasses to start a fire with glasses.

Nearsighted Glasses Don’t Work

The most important thing to remember is that nearsighted glasses will not start a fire. This type of lens is designed to disperse the light and not focus it. So, no matter how you move it or turn it in direct sunlight it simply will not create the intensely focused beam of light that you need.

Farsighted glasses will work as well as things like a fresnel lens or a magnifying lens. All of these can be easily carried. They even make small business card-sized fresnel lenses that can be stored in your wallet.

The Power of the Sun

The sun is insane! It is the most massive source of power, heat, and light that we have access to. In fact, we so underutilize and underappreciate the sun that I want to give you a factoid that will rock your world.

“Every two minutes, the energy reaching the earth from the sun is equivalent to the whole annual energy use of humanity. All the energy … the cars, lighting, and air conditioning of the world … in one year is equivalent to two minutes of the sun.”

Two minutes of sun enough to power a year’s usage of humanity | Environment – Gulf News

So, harnessing all this energy to start a fire is not really that tough. You can learn to do it in less than an hour.

Magnifying Sunlight to Make Fire

Sunlight burns wood, having passed through the magnifying glass
Sunlight burns wood, having passed through the magnifying glass

The first time I sat down with a lense and tried to harness the sun for fire-starting I was floored by how easy it was. I remember burning little pieces of my bootlace just by finding the sun and then honing in the light beams.

There is some skill to magnifying the sun. It’s not as simple as just finding the sun and letting the beam of light shine through a lens, There is the manipulation of the lens and the light.

  1. Remove your glasses in the midday sun and tilt the lenses toward the sun.
  2. Once you catch the sun’s rays in the lens place your hand underneath the glasses so the sunlight filtering through them hits your hand.
  3. Now, by raising the glasses away from your hand or moving them closer to your hand you would be able to control the size of the beam of light on your hand. You may need to tilt them a little back and forth too to get the best circle.
  4. Find the sweet spot and make the smallest brightest dot you can on your hand. If you do this part right the magnified sunlight will sting your flesh. You will make that dot so bright that it will hurt you.
  5. Now you can try it on a tinder nest. You could try it on a piece of char cloth or even just a piece of paper to see if you can make it smoke and glow. Be patient here and really learn the process of honing the light to its maximum.
  6. Once you feel confident in your ability to harness the power of the sun then you can gather the rest of the materials you need to build a fire and set it all ablaze.

The Importance of Tinder

It helps to have dry tinder to start a fire with glasses
It helps to have dry tinder to start a fire with glasses

Make no mistake about it the sun that comes through your glasses is hot enough to start a fire in any dry material. When I did this with my son he just piled up some leaves and caught them on fire. They all burned together quickly.

Still, that was a nice sunny hot day in the middle of summer. Getting this kind of fire to work for you on a clear day in the middle of winter might be a little harder. So, it is important that you have dry tinder. Things like dry wood shavings, dryer lint, cotton balls are examples of different types of tinder materials.

When you shine that magnified beam onto tinder-like this you will see smoke and you will have a fire. It happens fast if you have good tinder. That is what we want. We want fast and easy fire starting. If it’s an emergency situation and we need a heat source then time is of the essence.

A Technique for Mostly Ideal Conditions

While knowing how to start a fire with glasses can help you in a survival situation, you do need some superb conditions. You need that strong beam of light that comes around the middle of the day. It is that focused beam hitting your tinder nest that will create the fire.

However, if it is cloudy, raining, or even remotely overcast then this method will not work. If the sun is going down, it will not work. Of course, if it is nighttime and you have no sun then this method will also not work.

Whether you are using a fresnel lens or a pair of glasses, starting a fire with glasses using the sun requires a clear midday sky. So, this method should not be your go-to skill for fire starting. You would do better to carry matches, a lighter, or a ferrocerium rod. These tools work in bad conditions and the dark of night.

A Wilderness Survival Wizard

Try using a magnifying glass, fresnel lens or glasses to start that fire
Try starting that fire with glasses, a fresnel lens, or a magnifying glass

I never had the pleasure of nuking ants with a magnifying glass but I did start lots of fires as a child. I was a little bit of a pyromaniac. It pains me to know that I was in my 30s by the time I learned that I could have started a fire so easily without stealing my mother’s lighters.

In the midday sun, it is a lot of fun to pull out the glasses or a fresnel and capture and magnify the sun’s immense power. If you are low on matches or lighter fluid and you want to conserve that fire starting capability then it makes sense to use a method of starting a fire, like this one, because it literally costs you nothing.

Get out there in the sun and try to start a fire with glasses, a camera lens, or a fresnel. Once you get the technique you are going to feel like some kind of wilderness survival wizard!

Go here for more information about Campfires and Survival fires.