# Twelve Year Old Starts Lawn Fire with Magnifying Glass

**URL:** <https://boards.straightdope.com/t/twelve-year-old-starts-lawn-fire-with-magnifying-glass/845664>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [December 31, 2019, 1:14pm UTC](https://boards.straightdope.com/t/twelve-year-old-starts-lawn-fire-with-magnifying-glass/845664 "2019-12-31T13:14:50Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [January 3, 2020, 11:44am UTC](https://boards.straightdope.com/t/twelve-year-old-starts-lawn-fire-with-magnifying-glass/845664/21 "2020-01-03T11:44:44Z")

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Some years ago my parents had a love seat with chrome-plated legs, each leg being a flat piece of steel curled into a segment of a circle. One day shortly after they moved into a new residence, my sister walked in and promptly wondered about a strange burning plastic smell. After some investigation they tracked it down to this love seat. Turns out that late-afternoon sunlight had been hitting the curved surface of one of those chromed steel legs, and was being focused into a line on the vinyl-upholstered underside of that love seat, where it was melting and pyrolyzing the vinyl. A few more degrees, and it darn well could have caught fire.

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**Author:** ![Hilarity\_N.Suze](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hilarity_n.suze/32/6223_2.png) [@Hilarity\_N.Suze](https://boards.straightdope.com/u/Hilarity_N.Suze)\
**Post date:** [January 3, 2020, 8:31pm UTC](https://boards.straightdope.com/t/twelve-year-old-starts-lawn-fire-with-magnifying-glass/845664/22 "2020-01-03T20:31:27Z")

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> [@HelenGawn](#):
>
> Amateurs. Go find yourself a big-screen rear-projection TV and [do some foundry work.](https://www.youtube.com/watch?v=xyCH2T5PWUc)

Help me out here. I see a piece of glass smoldering on a black surface–is that the rear-projection TV screen? I also see a big Fresnel lens, which I would assume is the heat source, or rather, is refracting the heat source. What am I missing?

Don’t worry, I’m mature now and I do not have evil plans. You can tell me.

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