UV and Blue Light FAQs
|What are ultraviolet rays?
Ultraviolet (UV) rays are part of electro-magnetic radiation. They are invisible rays lying beyond the violet end of the visible spectrum.
Low intensity of UV rays are also emitted from fluorescent lamps, TV and computer monitors.
Are there different types of UV rays?
As different intensity (wavelength) of UV has different effect on us, they are commonly categorized as UV-A, UV-B and UV-C.
UV-C (wavelengths from 200nm - 290nm) is present above the earth's atmosphere and also given out from welding arcs. It also arises from sunlight's reflection from snow at high altitude.
UV-B (wavelengths from 290nm - 320nm) and UV-A (wavelengths from 320nm - 390nm) are present in our living environment, from direct sunlight or reflection from snow, water, sands, glass windows, concrete walls etc.
What are the harmful effects of UV rays on human eyes?
The effects and damages to the eyes from the UV radiation are well documented.
Since various ocular tissue layers absorb different wavelengths of the UV rays, they can respond quite differently.
The cornea is particularly susceptible to the effects of UV-C and lesser extent of UV-B. UV-C given off by a welding arc can be absorbed by the cornea and symptoms of foreign body sensation, tearing and pain may appear between 30 minutes to 12 hours after exposure. Excessive exposure has been documented to cause corneal cells damage.
Corneal absorption of UV radiation decreases dramatically at wavelengths above 290nm.
The portion UV-A and lesser extent of UV-B are transmitted through the cornea and aqueous, and nearly totally absorbed by the crystalline lens. Although painless, it can alter the lens nuclear proteins and lead to lens opacification (cataract).
Where light wavelengths in the range of 390nm to 445nm are termed as High Energy Visible light in the violet/blue band in the visible spectrum. HEV light has been claimed to be a cause of macular degeneration and damaging retinal tissues.
Pterygiums and Pingueculae have also been known closely associated to the exposure of UV rays.
Other than sunglasses, is there any UV/Blue light protection lens for spectacle wearers?
Normal human activities cannot avoid the eyes from exposure to the UV/Blue light. Sun ray is the greatest source of UV and Blue light, and although domestic fluorescent/LED lightings, TV and digital monitors emit very small amount of UV/HEV light, it's advisable to protect the eyes from the cumulative effects of UV/HEV light on long term exposure. There are special coatings or lens materials that shield 100% of UV and provide excellent HEV light protection for all day wear out and indoors.