Parameters:
(1) altitude
(2) reflection from snow, ice or water
(3) latitude
(4) protective measures taken (clothing and sunscreen)
(5) cloud cover
(6) season of the year
(7) time of the day
(7) personal susceptibility to light damage
The intensity of ultraviolet (UV) light increases 4% for each 1,000 feet above sea level.
intensity of ultraviolet light at a given altitude in feet =
= (intensity at sea level) * (1 + (0.04 * ((altitude in feet) / 1000)))
Snow, ice or water can reflect ultraviolet light, especially to surfaces normally covered, such as the underside of the nose and chin.
Light intensity is greater:
(1) as one gets closer to the equator.
(2) during the summer, but also during late spring and early fall
(3) during the mid-day sun (10:00 to 14:00 standard time, or 11:00 to 15:00 daylight savings time)
(4) when there is no cloud cover, partial cloud cover or a light cloud cover
Personal susceptibility to UV light depends on:
(1) skin type associated with the level of melanin (low risk in Blacks, intermediate to high risk in Whites, very high in patients with albinism), as described in the chapter on dermatology
(2) photosensitivity due to drugs or underlying disease
The presence of long sleeves on shirts and pants, socks, wide brim hat and sunscreen can reduce exposure to UV light. Wet clothing may transmit UV light, especially if the weave is loose. Eye protection is important, especially if there is there is glare from snow or ice.
