Green Power Science
A Fresnel lens is a type of lens invented by French physicist Augustin-Jean Fresnel (pronounced fre-NELL in scientific and lighting applications, although often pronounced FREZ-nell). Originally developed for lighthouses, the design enables the construction of lenses of large aperture and short focal length without the weight and volume of material which would be required in conventional lens design. Compared to earlier lenses, the Fresnel lens is much thinner, thus passing more light and allowing lighthouses to be visible over much longer distances.
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.
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