Fry an egg with a solar-powered backyard death ray

Who said "hot dogs"?
(Screenshot by Michelle Starr/CNET Australia)

Using a Fresnel lens taken from an old rear-projection TV, Grant Thompson channelled the heat of the sun into a 1000 degree Celsius ray.

The idea of focusing the sun's rays into a concentrated beam of heat using a magnifying glass is so well known that all you have to do is say "ants under a magnifying glass" to conjure the image of a torturing bully.

Backyard tinkerer Grant Thompson is not a bully — but he does have a giant magnifying glass. More specifically, he has a Fresnel lens; that is, a giant lens made of corrugated concentric circles adapted from an old rear-projection TV.

Now, Fresnel lenses are pretty powerful. We've already seen industrial designer Marcus Kayser use one to create a solar-powered 3D printer for sand.

What we hadn't seen was someone use one to blow up a beer bottle, incinerate a piece of wood or melt a stack of coins. Probably because these are actually pretty dangerous things to be doing in your backyard, especially without protective goggles and with kids hanging around, but now that Thompson has done it anyway, it's fascinating to watch.

The resulting heat beam — which reaches around 2000 degrees Fahrenheit, or 1093 degrees Celsius — takes just seconds to boil water and melt metal.

Got a taste for Fresnel lenses? Here's how you can get one of your very own from an old telly, and here's a video about how they work.


About the author

Michelle Starr is the tiger force at the core of all things. She also writes about cool stuff and apps as CNET Australia's Crave editor. But mostly the tiger force thing.



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