Often found at museum shops or stores that specialize in science products, Fresnel lenses come in squares, rectangles and circles. Invented in 1822 by Augustine Fresnel, a French physicist, the lenses concentrate light into focal points. The lenses are as small as credit cards and manufacturers have no restrictions on how large they make them. Does this Spark an idea?
Function
The initial use of Fresnel lenses occurred in lighthouses to intensify the light beams to assist boats and ships in foggy or stormy weather find the shore. Current uses include solar cooking, heat generation and as a lens in a rear projection television sets. Unlike a magnifying glass, the lenses are flat and do not result in any picture distortion in televisions. Scientists use the Fresnel lenses to experiment with light or change its color properties. People at large can use the lenses indoors to magnify small print, start campfires outdoors or melt glass or metal.
Considerations
When sunshine flows through a Fresnel lens, it concentrates into a small focal point that gets hot, depending on the size of the Fresnel lenses. Larger lenses reach higher temperatures than smaller lenses, since the focal points are longer and the lens gathers more light. Manufacturers use plastic materials to make the lenses and the larger lenses need to be placed in frames, typically wood, to keep them flat and rigid. When ordering a Fresnel lens, the dimensions given often refer to the grooved section, although some sellers include the mounting margins as part of the overall dimension. It's a good idea to contact the seller directly if you need a precisely sized lens.
Types
Besides their actual physical size, the lenses carry grades that describe their ability to concentrate light. The density of the grooves in a Fresnel lens affects its image and light-gathering potential. Higher density grooves result in better images, but a lower density of grooves is better for concentrating light, since the opacity is higher.
Warning
Although retailers sell the lenses in stores to any customer, the lenses are dangerous and should not be given to children who use them as toys. Even a small lens can start a fire quickly. No matter the size of the lens, it's a good idea to wear sunglasses or welding goggles when using the lenses outdoors, since the light is so concentrated. The lenses must be stored indoors away from sunshine.
Tags: Fresnel lenses, density grooves, Fresnel lens, concentrate light, focal points, good idea
