Passing UV Light with Different Types of Glass|
Article - January 10, 2016 By LarsonElectronics.com
Passing UV Light with Different Types of Glass
Ultraviolet (UV) light takes on a myriad of unique characteristics that are often misunderstood by most people. In order to avoid the harmful effects of UV bands, some manufacturers use different types of glass with UV-blocking mechanisms.
Keep reading to learn about the distinctive properties of UV wavelengths and superior variants of glass that are capable of blocking UV light.
Characteristics of UV Wavelengths
UV light is a special type of electromagnetic radiation that comes from the sun. Some luminaries, such as compact fluorescent bulbs and HID lamps, emit UV bands during output. Even LEDs (contrary to popular belief) emit very low levels of UV light. This type of light can be broken down into the following categories:
• UVA (Ultraviolet A): 315-400 nm
• UVB (Ultraviolet B): 280-315 nm
• UVC (Ultraviolet C): 100-280 nm
• NUV (Near Ultraviolet): 300-400 nm
• MUV (Middle Ultraviolet): 200-300 nm
• FUV (Far Ultraviolet): 122-200 nm
• H Lyman-a (Hydrogen Lyman-alpha): 121-122 nm
• VUV (Vacuum Ultraviolet): 10-200 nm
• EUV (Extreme Ultraviolet): 10-121 nm
Humans can’t see UV light because our eyes block bands in the 300-400 nm range, and shorter wavelengths are further filtered by the cornea. Some individuals without the natural lens can perceive NUV wavelengths, which appear whitish blue or violet. Out of all the UV bands on the list, UVA, UVB and UVC are the most common. UVA is not absorbed by the ozone, and can be found in black lights, such as bug zapper lamps. This type of UV light makes up over 95 percent of solar radiation that makes it to the surface of the Earth. UVB is a biologically active medium UV band that is easily absorbed by the ozone. Individuals that are prone to skin cancer should avoid UVB rays as much as possible, due to its contributions to skin aging and burning. UVC is a short wavelength light that is used to deactivate harmful bacteria. It is completely absorbed by the atmosphere.
UV Light and Windows
UV light is capable of penetrating common window glass found in most residential and commercial spaces. Such transparent surfaces are capable of blocking UVB rays, but not UVA bands. It is important to consider that UVA light can cause skin cancer and unsightly wrinkles. Because of this, some individuals develop freckles on the left side of their face from UV exposure while driving. Tinting windows can help block UVA light by up to four times.
Recent developments in the field of glass manufacturing has ushered in new technology that helps block harmful UV rays. These days, it is possible to block up to 99 percent of UV light, using a special film. Alternatively, some manufacturers mix robust materials with glass, which can improve its ability to block harmful UV light. The next section of this article expounds on UV-blocking efficiency rates of different types of glass.
UV Transparency Case Studies
The amount of UV light that glass will allow to pass through depends on its structure and combination of components used to make the product. A case study from the Department of Dermatology, Henry Ford Hospital, Detroit, Michigan; and the Department of Ophthalmology, Faculty of Medicine Siriraj Hospital, Bangkok, Thailand, highlights the efficiency of specific types of glass against UV bands. Titled Photoprotection by Window Glass, Automobile Glass and Sunglasses, researchers uncovered the level of transparency of the following surfaces:
• Clear Glass: Allows up to 90 percent of visible light, 72 percent of UV rays and 83 percent of solar heat to pass through.
• Tinted Glass (also known as heat absorbing glass): Absorbs between 40 to 50 percent of solar energy, including light transmission.
• Reflective Glass: Uses metal oxide coatings to create a reflective surface; significantly reduces both UV and light transmission.
• UV-blocking Coated Glass: Properties include thin, transparent surface. Capable of blocking up to 98 percent of UV radiation, while allowing all visible light to pass through.
• Laminated Glass: Manufactured by combining two types of glass together using a plastic interlayer. Capable of filtering up to 99 percent of UV light up to 375 nm due to the presence of a PVB interlayer. Wavelengths above 380 nm naturally passes through such surfaces. The thick properties of the glass also contribute to blocking soundwaves.
• Special UV-blocking Insulated Glass: This type of glass is manufactured using a piece of UV-blocking glass and low-emissivity (low-E) glass. It can block up to 99 percent of UV light, 70 percent of solar heat, while allowing up to 70 percent of visible light bands to pass through.
According to a published case study titled, The Role of Glass as a Barrier Against the Transmission of Ultraviolet Radiation: An Experimental Study, the thickness and color of glass may affect its ability to block specific types of UV bands and visible light. Glass with thick properties are capable of blocking more UV radiation. Green glass is known for being able to completely block UVA bands. Blue glass is inefficient in blocking UV light, allowing up to 56.8 percent of UV bands to penetrate the colored surface.
Low-E glass is a type of glass that effectively reflects heat. It is coated with a very thin, transparent material (thinner than human hair) that helps it reflect short and long-wave UV/infrared energy. This layer is typically composed of metal oxide and silver. Unlike other passive methods of UV light protection, low-E glass actively manages light and heat, like a thermos. The coating keeps interior conditions constant by reflecting temperatures back into the room. On a hot summer day, the glass may keep a room cool by allowing visible light to pass through, while simultaneously reflecting infrared (heat). During cold winter nights, low-E glass acts as an insulator by reflecting heat that is trying to escape back into the room.