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An L39 UV filter with a 55mm filter thread. UV filters are compounds, mixtures, or materials that block or absorb ultraviolet (UV) light. One of the major applications of UV filters is their use as sunscreens to protect skin from sunburn and other sun/UV related damage.
A UPF 30 fabric that blocks 29 out of 30 units of UV is therefore blocking 96.7%. Unlike SPF (sun protection factor) measurements that traditionally use human sunburn testing, UPF is measured using a laboratory instrument ( spectrophotometer or spectroradiometer ) and an artificial light source, and then applying a sunburn weighting curve ...
UV sunlight spectrum (on a summer day in the Netherlands), along with the CIE Erythemal action spectrum. The effective spectrum is the product of the former two. The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source.
The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared.
Windshield Sun Shades. Typically, the glass of the car's windshield itself blocks most of the UV light from the sun, and some of the infrared radiation.But it can't protect from the visible light that mostly penetrates through the window and gets absorbed by the objects inside the car.
An optical filter can be used to block out visible light and near-ultraviolet light. It is important to have a high transmittance within the solar-blind spectrum, but to strongly block the other wavelengths. [2] Interference filters can pass 25% of the wanted rays, and reduce others by 1000 to 10,000 times.
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[12] [13] [14] The UV-A light in a day of sunlight in a temperate climate is sufficient to break down most of the compound. Data presented to the Food and Drug Administration by the Cosmetic, Toiletry and Fragrance Association indicates a −36% change in avobenzone's UV absorbance following one hour of exposure to sunlight. [ 15 ]