Ultraviolet rays of medium wavelength (290~320 nm) usually have the greatest impact around noon, and are less destructive in the dark. The damage to the epidermis is obvious, which will cause sunburn and sunburn. The intensity of UVB-induced erythema is 100-1000 times that of UVA, so UVB is the number one killer of acute sunburn; in addition, together with UVA, it accelerates skin roughness and melanin deposition with skin aging.