The three main categories of materials that can be used for optics in UV applications are polymers, ceramics and glasses, and specialized UV glass compositions. Most greenhouse plastics are designed to block UV rays to a certain extent, but some modern plastics are designed to let UV light in, providing a more natural growing environment for plants. Low levels of UV rays in greenhouses help to keep parasites and insects away, and also protect the plant from long-term harm. Clear glass can transmit up to 90% of visible light and up to 72% of UV light, depending on its thickness.
Tight clothing can stretch and reduce the level of protection it offers, as the fibers separate and allow more UV light to pass through. Modern greenhouse plastics are manufactured to be resistant to UV light, protecting plants and helping the plastic last longer when exposed to sunlight. However, plants grow naturally outdoors and are exposed to UV rays, and studies show that almost all plants grow healthier and more fruitful when grown with UV light. The transmission of light in certain ranges of the spectrum is the ability of the material to let light through these ranges, which is measured by spectroscopy.
In addition, the UV transmittance of glass samples decreases as the Al2O3 content increases, and increases then decreases as the B2O3 content increases. In 1999, Kimlin and Parisi studied solar UV radiation transmitted through normal and tinted car windows and found that tinting glass provided significant protection against UV radiation. Blocking UV light can make it harder for greenhouse plants to fruit, but it helps them last longer overall. Since plastic and glass materials installed in windows and decorative panels can reduce people's exposure to UV rays, it is important to measure the irradiance they transmit.
Not all greenhouse plastics block UV rays, as blocking them isn't always the best way for satisfactory harvests. Due to increased demand for sanitation measures related to COVID-19, procurement activities have increased, including the search for suitable materials such as fused silica glass which is highly resistant to temperature and transparent to UV rays for ultraviolet light applications. Glass is somewhat effective at blocking UV rays, especially harmful ones, and is completely resistant to them. All plants are damaged by UV light over time, so blocking it can be beneficial for greenhouse plants.
People who work with or around materials that let through UV light should take precautions against overexposure. Wearing protective clothing or eyewear can help reduce exposure levels significantly. Additionally, using materials that block or filter out certain wavelengths of UV light can help protect people from overexposure.