Heating wood with a Fresnel lens. Close-up footage of sunlight being focused onto a piece of wood with sufficient power to cause the wood to burn. The sunlight has been focused through a Fresnel lens. Fresnel lenses have a structure that allows them to be made much thinner and larger than conventional lenses. One application of Fresnel lenses is for solar power, as they can concentrate sunlight onto solar cells in a ratio of 500:1.