Solar Fresnel Lens
The King of Random YouTube channel does have some great DIY ideas despite the mainstream, uninteresting content that the channel has recently begun to produce. One of my favorites, one that I was lucky enough to have the opportunity to replicate, is their “Solar Scorcher” project which just uses a large Fresnel lens from an old projector TV to focus one to two square meters of the sun’s light down to a point the size of a penny. The power of the light hitting the Earth’s surface, with the sunlight hitting perpendicular to the surface, peaks at around 1000 watts per square meter. This is reduced from nearly 1400 watts before the light passes through the atmosphere but is still unbelievably powerful. A two square-meter large Fresnel lens is capable of focusing 2000 watts of solar light down to the size of a penny, effectively melting the hypothetical penny into a puddle in around three seconds.
I have acquired three such Fresnel lenses thus far, but only one is clear enough to be used effectively, having a glossy backside instead of matte, where matte scatters the light from the TV projector in a more natural way for TV-watching but prevents clear focusing and causes lots of light to dissipate when trying to use it as a lens. Coincidentally the one that works best as a focusing lens, by far, is also the largest lens that I have, at close to two square meters of cross-sectional area. To provide a surface on which to lay objects below the lens, we slid a block of concrete under the focal point, but the two kilowatts of photon power melted the concrete into an orange glowing, bubbling, popping liquid in a matter of minutes. Potentially this could have applications where extreme temperatures are required, but for us it was more of a fun but dangerous party trick.
Capable of lighting fire to a wooden surface nearly instantly, melting coins and burning a hole through an ear of corn, a Fresnel lens is easily the most powerful large-scale magnifying device that a consumer can find. Luckily for enthusiasts like me, they were mass produced for projector televisions, and now is the perfect time to find them literally being thrown out on the street because that style of TV is obsolete. I am always searching for more lenses, as like microwave transformers, they have a good number of potential applications. I still have yet to construct a wooden frame for my lens, but I will be doing so in the near future, once I have a place to store the structure.
Right now, the lens is mere millimeters thick and so it can be stored in any number of places easily, but in order to get the rigidity necessary to hold the lens planar and perpendicular to the sun’s rays, it needs a frame. For it to function properly as a lens it needs to be as flat as possible, assuming that there are no biased manufacturing defects. Using wood to build the frame will allow it to be both quite rigid and light, so maneuvering it won’t be as dangerous or as much of a hassle. Until I do build the frame, which I will most likely first mock-up in Creo, I don’t plan to use the lens, but am keeping it safe from scratches and dust. It is made of plastic after all, and the patterned surface of the lens is extremely susceptible to scratching which in the end will reduce the power output of the lens.