Fresnel Lenses can be a Useful Tool for Preppers

Fresnel lenses

The Fresnel lens set in its wooden frame.

The other day a friend gave me a Fresnel lens that he removed from a projection television.  It is huge, it measures 50 inches by 37 inches.  We took and installed it in a wooden frame and have been experimenting with it.  Now many of you may be familiar with the small Fresnel lenses that come in many survival kits as a fire starter.  They measure approximately 3 ¼ x 1 ½ inches and are very close in size to a business card.

I have had small one for years in a pocket survival kit that I often carry.  If the sun is out, they will start a fire.  Now Fresnel lens can be made much thinner than a comparable conventional lens and can be made flat.

Fresnel lenses

Here you can see the difference in size between the small Fresnel lens used in the survival kits and the big one.

The big ones have many uses that partially depend on the type that you have.  I understand that both types come in TVs and you don’t know what you have until you try them out.  The two types are

Spot

A spot Fresnel lens uses multiple flat segments, arranged in a circle, thus focusing light on a small spot.  This type does not produce a sharp image, but has application in solar power, such as focusing sunlight on a solar panel.

Linear

A linear Fresnel lens uses multiple flat segments, arranged linearly, thus focusing light on a narrow band.  This type does not produce a sharp image, but has application in solar power, such as focusing sunlight on a pipe, to heat the water within:

Fresnel lens

The Fresnel lens heating water.

You have to be very careful with these lenses; some of the spot lenses will produce enough heat to melt a penny, and can very easily burn your hand.  Some of the linear are safer to use, since they defuse the heat.  The big one I have is a linear.  The small ones that come in survival kits are spot.

I have been playing with mine in the backyard.  The first thing you need to do is to determine its focal length.  The focal length is the distance from the lens to the point at which it generates the most heat.  Since mine is a linear it forms a line and not a spot. This shows you how far you need to set the object you want to heat from the lenses.

Since plastic Fresnel lenses can be made larger than glass lenses, as well as being much cheaper and lighter, they are used in industrial applications to concentrate sunlight for heating in solar cookers, in solar forges, and in solar collectors used to heat water for domestic use.  Some Fresnel lenses can concentrate sunlight (with a ratio of almost 500:1) onto solar cells.

So far, we have been able to heat water on a cool sunny day just by setting a pan on the ground and focusing the lens on it.  In the next few days, we plan to build a frame to make it more practical to use.

Fresnel lenses

The Fresnel lens charred this 5/8 plywood in approximately 10 seconds. Notice how the char is in a straight line. Be careful these can be very dangerous.

Now there are some dangers in working with these.  Mine will make a line so bright you need welder’s goggles, and so hot, it can almost instantly char a piece of plywood.  You have to be careful where you store these, people have burned their houses down by leaving them where the sun can reach them.

In the near future, we plan on doing a bit of experimenting with mine to determine the limits of it capabilities.  I can see possible use for them in solar cooking, purifying water and in melting glass and some metals such as lead and copper.

We will post more on these in the future.

Howard

 

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17 Responses to Fresnel Lenses can be a Useful Tool for Preppers

  1. Sam P. says:

    Can you take the Fresnel Lenses out of a smaller tube TVs? If so how?

    • admin says:

      As far as I know they only come from projection type TV. There are other sizes and types of Fresnel lens available for sale on the internet. But if you can find an old projection TV that is the cheapest. The lens is right at the front behind the protective screen.
      Howard

      • bubster says:

        Lenses from older projection TVs seem to work best. Treat these lenses like a lit torch. Use an old sheet to cover them to avoid burning your house down.

  2. Peter says:

    Hello Everybody,
    We have replaced our windows in our house, with the old windows, how can they be useful for different projects.
    Thanks for the warning, i placed the windows against the house, not knowing what danger it will cause during the summer, maybe regular glass not, anyway i removed them, just to be on the safe side.
    Peter

  3. Becky says:

    IF you were careful, and aimed the line at rock, could you use this as a heat source? the sun would warm the rock, and the rock would radiate that heat into the space you are trying to heat?

  4. Phil says:

    I started learning about fresnel lenses by watching videos at https://www.youtube.com/user/GREENPOWERSCIENCE.

    You don’t have to spend a lot of money either. Go to Amazon.com and search for “fresnel lens” and you can buy 8.5 x 11 inch lenses for $7 to $10. I got mine at Office Max.

    I am the magic man of the neighborhood and the local kids love me. I use my “sheet of paper sized” lens to ignite paper instantly, boil water & vegetables quickly, and burn holes in wood pieces. My “magic tricks” have also given me the chance to talk to parents about preparation by introducing them to this unorthodox way to light fires and boil water.

    I have fresnel lenses in my basement, my camping gear, my prepper gear and in my bug-out bag. As long as the sun is shining, I can start a fire or boil water for drinking or cooking. I’ll never be without one.

  5. Harry Gilder says:

    Thanks for the info Phil. Good luck with the parents. Don’t give up either, they’re worth it. Harry

  6. Chuck Findlay says:

    I have 2 of these leaning against the garage, I play with them avery so often. I have not found a use for them yet, but see them as useful down the road. The big one is out of a 50-inch TV and on a hot summer day, it will make blacktop bubble in just a few seconds.

    You really need welding goggles to play with these as the spot is very bright.

    U-Tube has several videos of people making mostly useless projects with these lens. Neat to play with, but still useless.

  7. Michael Williams says:

    Great – but frustrating that it is impossible to find out where such big lenses can be bought. As much as I notice in China only! I would need it for an art project.
    Do you have a source? Thanks in advance.
    Mike

    • Kidd says:

      You can find them on ebay. I have three very nice large spot lenses I found in old tv’s. I’ll sell you one for a good price if you cant find one elsewhere.

  8. Ed Harris says:

    Best Glide ASE has a credit card sized fresnel lens of 2″x3.25″ in protective slip-case:

    http://www.bestglide.com/fresnel_lens_firestarter.html

    Perfect to carry in your wallet or to tape inside the lid of your Altoids survival tin. It should not be your only primary fire starter, but is a great backup which will fit anywhere. It is small, flat, light and cheap. Practice IS required. You need a sunny day for it to work. Best Glide’s version has 4 power magnification, rather than the more than common 2X of typical credit card magnifiers.

  9. Rehan says:

    Im making project on solar cooking using fresnel lens.what type lens should i use.linear or spot?

  10. is it possible to cast an arrowhead with molten rock? or maybe with glass? I want to make a few of them to scatter in a site where arrowhead are hunted!

  11. Does size of lens (60 inch diagonal) make a hotter ray then A 19 inch lens? I have both but not sure which one to use to melt rocks for casting arrowheads

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