How to Start a Fire With Just a Magnifying Glass

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Use the power of the sun to light a spark

Co-authored by Luke Smith, MFA

Last Updated: April 29, 2024 Fact Checked

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Starting a Fire

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Selecting Tinder

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Understanding the Science

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Q&A

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Warnings

Creating fire with a magnifying glass is a fun science experiment and also a handy survival skill. It’s easy, too—just use the magnifying glass to concentrate the sun’s heat onto some tinder, like newspaper, which will soon spark a fire. We’ll show you how to do it in greater detail, and fill you in on the best tinder to use for your magnifying-glass fire. Then, to round out this fiery experiment, we’ll show you the science behind how it works.

Things You Should Know

Place dry, flammable tinder on a fire-safe surface, like concrete or bare dirt, under direct sunlight.
Hold the magnifying glass perpendicular to the sun’s rays, so that the sunlight travels through the glass onto the tinder.
Adjust the angle of the glass and its distance from the tinder until the light forms a small bright dot. Hold the dot still for 20-30 seconds until it starts a fire.

Section 1 of 3:

Starting a Fire

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1
Find a spot with full sunlight and little wind. You’ll need the right conditions in order to start a fire with a magnifying glass. Move to a spot that receives full, strong sunlight. Keep away from shaded areas and, ideally, start your fire on a day with few clouds overhead.^{[1]
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Research source} Also, find somewhere with little to no wind or breezes, which may extinguish your fire before it starts.
- Before you begin, put on a pair of sunglasses to shield your eyes from the bright, concentrated light made by the lens. Safety first!
2
Hold the magnifying glass between the sun and the tinder. Place flammable tinder, like newspaper, on the ground. Hold the magnifying glass perpendicular to the sun’s rays, so that the sun shines through the glass onto the tinder.^{[2]
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Research source} You’ll notice a small, bright dot appear on the tinder. Bring the magnifying glass closer to the tinder to make the dot as small as possible—you may need to adjust your distance from the tinder, as well as the angle of the magnifying glass. Tilt it back and forth until the bright spot is just a small pinpoint.
- Aim to focus the circle until it’s only about ¹⁄₄ inch (0.64 cm) across. The angle at which you hold the lens varies by where the sun is in the sky—just be sure the lens is perpendicular (90°) to the sun’s rays.
- Also, find somewhere without fire hazards to start your fire, like a concrete surface. If you’re in the woods, look for a fire pit, or brush any dry vegetation away to start your fire on the bare dirt.
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3
Focus the dot of light in one place for 20-30 seconds. Hold the magnifying glass still until the tinder begins smoking. Lighting a fire with a magnifying glass takes a bit more time than using a lighter or a match, so be patient!^{[3]
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Research source} Keep the circle of concentrated sunlight as still as possible in order to build up heat on the tinder. If you move the circle around on the tinder, the heat won’t be able to start a fire.
- If you’re creating a fire on a day without strong, direct sunlight, it may take more than 5 minutes for the tinder to catch on fire.
- Note that if it’s a particularly cloudy day, or there’s no strong, direct sunlight, you may not be able to start a fire with your magnifying glass.
4
Arrange your tinder inside kindling and other fuel to start a campfire. If you’re building a fire for survival, or just to toast marshmallows around, arrange some dry, pencil-sized sticks in a teepee shape. Once you ignite your tinder, use heat-proof gloves or tongs to place it inside the kindling of dry sticks (or ignite it while its already inside). After that’s caught fire, place dry firewood in a larger teepee shape around it to keep the fire going.^{[4]
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- Typically, you need an armload of kindling for each campfire you start.
- When you’re done, extinguish the fire with 4-5 shovelfuls of dirt, or water from a garden hose or bucket.

Section 2 of 3:

Selecting Tinder

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1
Use a few sheets of newspaper as tinder if you have some nearby. If you’re looking to start a campfire, first you’ll need to make tinder. Newspaper burns easily and is often used to make commercial fire starters.^{[5]
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Research source} Take 2-3 sheets of newspaper and tear them each into 3-4 pieces. Then crumple each of the newspaper pieces into a ball, which you’ll focus the magnifying glass onto to start your fire.
- If you don’t have newspaper, use paper towels as tinder instead. They’ll burn in practically the same way.
2
Use a piece of char cloth for tinder for a very flammable option. Char cloth is made from fabric that has already been charred. Consequently, it ignites at low temperatures compared to other types of tinder.^{[6]
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Research source} This makes char cloth an ideal type of tinder to use when starting a fire with a magnifying glass. You can use char cloth as a tinder on its own, or pair it with another tinder (e.g., newspaper or pine needles) to ensure that the second tinder catches fire.
- Char cloth is widely available at outdoors stores, or you might make your own char cloth using a metal tin, a heat source, and white fabric.
- You might also use cotton balls or dark-colored fabrics (which absorb heat more easily than light-colored fabrics) as tinder.
3
Collect coarse, dry, natural tinder if you’re building a bonfire. If you’re building an impromptu fire in a rural or secluded area, gather dry leaves, grass, or pine needles to start a fire. Dry bark also burns well—find a tree with loose, fibrous bark, and tear 2 or 3 handfuls off. Before starting your fire, shred the leaves or bark into small pieces with your hands so that the tinder will catch fire more easily.^{[7]
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- Make sure that natural substances are dry before you attempt to light them on fire. Wet leaves or pine needles will smolder and smoke, but never actually burn.

Section 3 of 3:

Understanding the Science

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1
Magnifying glasses concentrate energy into a small area to create fire. The curved (or “convex”) surface of the magnifying glass redirects light into a small dot. That light is made up of photons, or tiny particles of energy. When those photons are concentrated through the magnifying glass, their energy is all focused on a small area. All that crowded energy in such a small area creates heat, which in turns creates fire!^{[8]
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- Photons carry electromagnetic radiation, or energy waves that include light. Light itself exists on the electromagnetic spectrum (also called the color spectrum), as a visible form of electromagnetic energy.
2
Experiment with different kinds of lenses to make fire. There are a number of different objects that use lenses similar to the glass in a magnifying glass—binoculars, reading lenses, and eyeglasses, just to name a few.^{[9]
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Research source} If you’re in a survival situation (or just want to experiment and see how different lenses concentrate those photons), try starting a fire with any convex lens you might have. Glasses typically work best!
- Some glasses lenses are only curved on 1 side, so it might be tricky to start a fire with them alone. But add a drop of water to the flat side and, voila! They’ll work just like a magnifying glass.

Community Q&A

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Question

What is the fastest way to burn something with a magnifying glass?

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The fastest way to burn something with a magnifying glass is to use newspaper. The easiest part to start a fire on a newspaper is an area on which there is a lot of black ink, like in the black and white photos, etc.

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How hot does the temperature have to be to burn the paper?

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Paper burns at 451 degrees Fahrenheit, or 233 degrees Celsius.

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Will this work if it is cold but there is sun?

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Yes. It may just take longer.

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Warnings

Do not look directly at the sun when trying to locate it in the sky. Also, never look at the sun through your magnifying glass.

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Never direct the heat from the magnifying glass onto your skin.

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Have water nearby to douse the fire in case of an emergency.

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