Classification of UV ultraviolet light
By biological effect, ultraviolet is divided into four wavelength bands:
UVA band, wavelength 320-400nm, also called long-wave black-spot ultraviolet. It penetrates strongly and passes most clear glass and plastics. Over 98% of long-wave UV in sunlight reaches the earth through ozone and clouds; UVA reaches the dermis, damaging elastic and collagen fibres and tanning the skin.
Harm to humans: over 95% of UV that reaches daily skin is UVA, so it causes the greatest skin damage. UVA crosses the epidermis into the dermis, hitting collagen and elastin; dermal cells protect poorly, so small UVA doses already harm. Over time: sagging, wrinkles, visible capillaries.
It also activates tyrosinase, causing immediate melanin deposition and new melanin, darkening dull skin. UVA causes long-term, chronic, lasting damage and premature ageing - hence "ageing rays".
Applications: 360nm UVA matches insect phototaxis curves for insect lamps. 300-420nm UVA through special glass that cuts visible light radiates near-UV centred on 365nm for mineral ID, stage effects, banknote checks, etc.
UVB band, 275-320nm, also mid-wave erythemal UV. Moderate penetration; shorter parts are absorbed by clear glass. Most solar mid-wave UV is absorbed by ozone; under 2% reaches the surface, strongest in summer and afternoon.
Harm: UVB causes erythema, aids mineral metabolism and vitamin D, but long/excess exposure darkens skin and causes redness and peeling. It oxidises the protective lipid layer (dry skin), denatures nucleic acids/proteins in epidermal cells (sunburn), and heavy exposure raises cancer risk.
In addition, long-term UVB damage can mutate melanocytes and leave hard-to-remove sun spots.
Applications: UV health lamps and plant-growth lamps use special UV-transmitting glass (blocking below 254nm) and phosphors peaking near 300nm.
UVC band, 200-275nm, also short-wave germicidal UV. Weakest penetration - cannot pass most clear glass or plastics. Solar short-wave UV is almost fully absorbed by ozone.
Harm: short-wave UV is highly harmful and must not irradiate people directly; brief exposure can burn skin, and long/high intensity raises skin-cancer risk.
Applications: UV germicidal lamps emit UVC. Short-wave UV is widely used in hospitals, HVAC, cabinets, water treatment, drinking fountains, sewage plants, pools, food/beverage packaging lines, food/cosmetics/dairy/brewery/bakery plants and cold rooms.
UVD , 100 200nm , vacuum .
185nm UVD ultraviolet turns O2 in air into ozone O3; ozone's strong oxidation effectively kills bacteria.
But 185nm UV itself does not disinfect. Ozone's diffusion offsets UV's straight-line limits and dead corners, reaching any space with the air for more thorough sterilisation.
