Giant Fresnel lenses

[Num7]

Giant Fresnel lenses

I found this today, there's some interesting stuff about these giant fresnel lenses. They concentrate solar power like a magnifying glass.
It could be useful when there's no electricity, except at night. On Ebay, they're around 100.00/200.00$.

​

[FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular] When placed in the sun, a fresnel lens will act as a giant magnifying glass and concentrate light to a very small point. Most large fresnel lenses will concentrate several square feet of sunlight to less than an inch resulting in a hot spot over 2000 degrees Fahrenheit. This will cause wood to instantly catch on fire or zinc and copper metal to melt in a few seconds or even burn and vaporize. We have boiled 12 oz. of water in a dark glass bottle in 90 seconds and burned a hole in a stainless steel bowl.. One gallon of water was boiled in 30 minutes.[/FONT]

GREEN POWER SCIENCE WOULD BE NICE ON THE DISCOVERY NETWORK
SOLAR COOKING WITH THE SUN OUTDOOR LIVING PARABOLIC FRESNEL LENS LENSE
HOW TO FRESNEL LENS STAND

If well used, you can cook, melt stuff, run a sterling engine, etc.
There are some videos on Youtube here. There are also many videos in the links above.

Do you guys have ever seen one of these lenses in real life ?

Num7

 

[kcwildman]

Re: Giant Fresnel Lenses

never even heard of one befor
it kindah looks like thescreen protector lens off my old big screen tv.
I let the kids tear it up when it died, they found a plastic film mirror from the back wall of the unit(projection type) some magnets, and a lens that looks just like it. huh I'll have to play with it and see if it is one, I doubt it is. but we shall see.

 

[Num7]

Re: Giant Fresnel Lenses

I'll try to find some of these during my vacation time.
I don't expect to get a big one, but If I can, maybe I'll get a small cheaper one.
We can burn some paper with a small magnifying glass, so I don't need a 3' wide fresnel.

Don't look at the sun through that lens !

 

[kcwildman]

Re: Giant Fresnel Lenses

no shit dude at 2000 degr.
we are talkin french fried to charred ash, quick,fast,in-a-hurry like.
cool let us know what it will do.
I haven't fooled with the tv lens yet, but its been rainin for ten years round here. quack,quack,quack waddle,waddel

 

[Num7]

Re: Giant Fresnel Lenses

lol It's rainin here too. It's been pretty crazy yesterday.
I'm not sure to get that lens. I'm not gonna order it over the internet. If I see one somewhere around me, maybe I'll give it a try.

Num7

 

[jurgen36]

Re: Giant Fresnel lenses

You could buy them in Takilag that is a border town between Burma and Thailand for about 250 baht which is approximately 8 US dollars. They were rolled up and made out of thin plastic and were approximately 1.3 square meters in size. You did have to make your own frame to mount them. They also sold ultra high power zappers with rechargeable batteries. They made sparks a good 10 inches long. We used them to kill rabid soi dogs. I would not try to use them on people. The price was 500 baht or about 15 to 16 US$.
Regards

 

[EachPeachPearPlum]

Re: Giant Fresnel lenses

Though it is a work of fiction, Baxter's and Clarke's "Sunstorm" deals with the absolute epitome of a "Giant Fresnel Lens".
A lenses in constructed in space to act as a large parasol to shade the earth from a catastrophic concentration of sunspot activity. One side of the lenses is constructed out of glass created from melting sand on the moon. The final product of the Fresnel ultimately allows the heat to be focused elsewhere.
With that in mind, couldn't this be adapted to lessen the affects of global warming? Yes, it would be large, and take a painstakingly long time to complete, but time passes regardless.
Personally I love the technology Clarke creates in his books, and think its a wonderful idea.

 

[jurgen36]

Re: Giant Fresnel lenses

Though it is a work of fiction, Baxter's and Clarke's "Sunstorm" deals with the absolute epitome of a "Giant Fresnel Lens".
A lenses in constructed in space to act as a large parasol to shade the earth from a catastrophic concentration of sunspot activity. One side of the lenses is constructed out of glass created from melting sand on the moon. The final product of the Fresnel ultimately allows the heat to be focused elsewhere.
.

Also what a weapon this would make, you could burn up any city on earth, there is no defense possible.
Regards

 

[EachPeachPearPlum]

Re: Giant Fresnel lenses

Also what a weapon this would make, you could burn up any city on earth, there is no defense possible.
Regards

Now thinking it over...a frensel lenses could neither be used as a solution for global warming, or as a weapon. Global warming occurs within the atmosphere.
A frensel lenses could not be used as a weapon because of the rip it would create in the atmosphere. If you think about the concentration of radiation entering the atmosphere at a focused point, the o-zone layer would be destroyed. Usually, in space-flight launches holes are ripped in the atmosphere, but this is only for a brief amount of time before it mends itself. In the case of shuttles you are dealing with projectiles aero-dynamically designed to enter the outer-sphere and minimalize the effects of breaking through the barrier. A weapon would be considerably larger than a shuttle (if it were to be effective and have purpose) so the recovery of the atmosphere would take a longer time, allowing other foreign substances to enter the Earth's atmosphere, and equally allowing the Earth's atmosphere to loose some of its precious balance. The effects would probably be lasting, and wouldn't only affect the targeted area.

 

[Num7]

Re: Giant Fresnel lenses

What if they try it on Mars, what kind of effect could it have on the atmosphere there ?