Definition of solar UV radiation
Solar UV radiation is divided in to three types, based on wavelength: UVA (320–400 nm); UVB (290–320 nm); and UVC (200–290 nm). Solar UVC does not reach the earth's surface as it is absorbed or scattered in the atmosphere. UVA and UVB are of concern because of their potential to cause skin and eye damage. Both UVA and UVB are associated with the development of skin cancer[1][2][3].
Transmission of UV radiation through glass
All types of commercial and automobile glass block the majority of UVB, but the degree of UVA transmission depends on the type of glass[4]. While the thickness of glass does affect UV radiation transmission, the effect is limited compared with other factors[5].
Vehicle windscreens and side windows
UV radiation levels inside a car vary depending on factors such as whether the side windows are open or closed and the position of the vehicle in relation to the sun. UV radiation levels are generally much lower inside the vehicle than outside in full sunlight[6].
Laminated glass, used for windscreens, and tempered glass, usually used for side and rear windows, both block UVB radiation[4][6]. However, UVA transmission depends on the type of glass. Laminated windscreens, made from a tough plastic layer bonded between two panes of glass, provide better protection against UV radiation compared with tempered glass, blocking about 98% of UVA radiation[6].
In comparison, tempered glass, used for side and rear windows, allows the transmission of substantially more UVA radiation. However the amount transmitted can vary widely depending on the thickness and colour of the glass[4]. Estimates of UVA transmission through tempered glass range as high as 79%[6].
Clear or tinted films can reduce the amount of UV radiation penetrating through the side glass by over 99%[6]. Alternatively, fabric side window covers can provide shade and UV protection. The amount of protection varies with different products. Tints and covers are only effective in providing protection against UV radiation when windows are closed.
Film and tint applied to car windows must meet state and territory regulations. All states and territories in Australia stipulate a maximum darkness, known as the visible light transmission level (VLT) for the windscreen, and side and rear windows. Windscreens are not to be tinted as the minimum requirement for VLT is 75% and even clear film reduces VLT below 75%. The Window Film Association of Australia and New Zealand website has information on regulations.