Why are the bottoms of windmills green? (This doesn't work so well in the spring, when the crops are green.) German windmills are sometimes painted dark green at the bottom to blend into the forest. European rotors usually have a red stripe to make them visible to aircraft.The sight of a windmill is an iconic symbol of sustainability and clean energy. They harness the power of wind to produce electricity, and their large blades spin gracefully in the air. However, you may have noticed that the bottoms of windmill blades are often painted green. You might wonder why this is so. In this essay, we will explore the reasons behind this peculiar aspect of windmill design. The answer to this question lies in the science of light and color. Specifically, it has to do with the way that light interacts with the materials that windmill blades are made of. Windmill blades are typically made of fiberglass, which is a type of plastic reinforced with glass fibers. Fiberglass is a popular material for windmill blades because it is lightweight, durable, and can be molded into complex shapes. However, it is also susceptible to a type of degradation called UV degradation. UV degradation occurs when ultraviolet (UV) radiation from the sun breaks down the chemical bonds in a material. This process can cause the material to become brittle and weak, which is obviously not ideal for something as important as a windmill blade. To prevent UV degradation, windmill manufacturers often coat the bottoms of their blades with a green-colored gel coat. This gel coat contains a substance called a UV stabilizer, which helps to absorb the UV radiation from the sun before it can penetrate the fiberglass and cause damage. The choice of green as the color for the gel coat is not arbitrary. Green is the color that is most effective at absorbing UV radiation. When light strikes a material, it can either be absorbed, transmitted, or reflected. Different colors of light have different wavelengths, and some wavelengths are more effective at penetrating materials than others. Green light has a wavelength of around 550 nanometers, which is right in the middle of the visible spectrum. This means that it is not easily absorbed or transmitted by most materials. Instead, it tends to be reflected. By coating the bottoms of windmill blades with a green-colored gel coat, manufacturers are essentially increasing the amount of green light that is reflected off the surface of the blades. This helps to reduce the amount of UV radiation that is absorbed by the fiberglass, and thus reduces the risk of UV degradation. In conclusion, the reason why the bottoms of windmill blades are often green is because of the science of light and color. Green is the color that is most effective at absorbing UV radiation, which is important for preventing UV degradation in the fiberglass blades. By coating the bottoms of the blades with a green-colored gel coat, windmill manufacturers are able to increase the amount of green light that is reflected off the surface of the blades, which reduces the amount of UV radiation that is absorbed. This is just one example of the many ways that science and technology are used to make renewable energy sources like wind power more effective and sustainable.