Recommendations for protection when the day’s predicted UV index is at various values are:
UVA is a long wavelength ultraviolet ray from the sun. UVA rays are the “aging” rays in the UV spectrum. UVA radiation ranges from 320 to 400 nm in wavelength. Some wavelengths in that range have greater potential to cause damage than other wavelengths. UVA radiation is stronger in the early morning and late afternoon when the sun’s rays reach the Earth at an angle.
UVB is a medium wavelength ultraviolet ray from the sun. UVB rays are the “burning” rays in the UV spectrum. UVB radiation ranges from 280 to 320 nm in wavelength. Some wavelengths in that range have greater potential to cause damage than other wavelengths. UVB radiation is stronger between late morning and early afternoon when the sun’s rays are directed straight down at the Earth.
SPF stands for Sun Protection Factor. It is the ratio of UV radiation dose required to produce recognizable redness on skin that has been protected with a sunscreen from the UV radiation dose required to produce the same redness on unprotected skin (using a clinical test procedure on human skin). SPF tells you how much longer it will take for your skin to begin to redden with the product on than if your skin was unprotected. The percentage of burning UV rays that a product blocks does not increase proportionally with the SPF value. So SPF values indicate a function of skin reddening.
UPF stands for Ultraviolet Protection Factor. It is the ratio of the average effective ultraviolet radiation (UVR) irradiance transmitted and calculated through air to the average effective UVR irradiance transmitted and calculated through fabric. In other words, it is the amount of ultraviolet radiation that a fabric blocks. Hence UPF values are used in the Fabric’s UV transmittance test by spectrophotometer equipment.
Sun protective clothing
Sun-protective clothing is any garment that can provide adequate protection from the sun. Generally speaking, clothing must have a UPF value of 15 to 50+ (blocks 93 – 98% of UV radiation), and cover or shade sufficient skin to protect a person from the damaging rays of the sun.