Even stone can melt, and concentrated sunlight can generate temperatures exceeding a thousand degrees—this is the marvel of the Fresnel lens.

Fresnel lenses are typically made of plastic or glass; one side is highly polished, while the other features a series of tiny, evenly spaced convex lenses that increase in size, creating a helical texture.

I’m sure many of you have tried using a magnifying glass to focus sunlight, which can quickly raise the temperature to very high levels.

When I was a kid, as soon as I learned about the magnifying glass’s ability to focus sunlight, I’d immediately start conducting all sorts of destructive experiments—lighting matches, burning paper and wood, even setting ants on fire. Pretty soon, the ants would stop moving altogether. I’m sure plenty of you have done the same thing, too.

However, when it comes to focusing light, a certain type of lens is far more effective than a magnifying glass—this lens is called a Fresnel lens.

What is a Fresnel lens?

In fact, the name itself gives you a clue: it was invented by a Frenchman named Fresnel, and its shape resembles concentric spirals, which is why it is also known as a spiral lens.

Although we may not encounter Fresnel lenses very often in our daily lives, they are widely used in a variety of fields, including national defense, aviation, transportation, industrial manufacturing, and civilian applications.

Key words:

Fresnel lens