IS ELECTROMAGNETIC RADIATION REALLY THAT DANGEROUS TO YOUR EYES ?
Unfortunately there are more than a few opticians who don’t actually know a whole lot about eye care .
This is a very short and sweet summary to get the main points out on eye protection from Electromagnetic Radiation.
ELECTROMAGNETIC RADIATION ( EM)
When we talk about E.M, it is pure energy , Simply Light -no mass. No form, travelling at the speed of light. 300,000,000 meter per second. Fastest speed possible in universe. we could see only 0.0035% of EM rays.
Sun is the only source which can emit entire electromagnetic spectrum.
Is it a wave ? or Is it a particle?
It is both.
Let me explain,. If a blind man happens to touch the legs of an elephant, he feels it as a strong Tree. If he touches the stomach of elephant, he thinks it as a flat rock. And if he touches the tail, he thinks it as a snake. Same elephant, different feelings. In the same way, you can take EM as a wave or particle. In fact it is wave-particle duality.
Wave Particle duality means, particle and wave nature exist in EM. I consider it as Ardhanarishwar!! When you make the male and the female in to one, so that male not be male and if female is not female, then it become Ardhanarishwar!! Yes He is God. Indians look at sun, and worship him.
So we understand EM has both wave characteristics and particle characteristics at the same time.
It is a stream of photons.
As this article is on eye health , particle mode is given more importance . Because in Retina photoelectric effect take place. Wave mode doesnot work for photo electric effect. In fact Retina accept light as a wave and transfer the absorbed energy to a particle electron that is used in subsequent electronic image formation process.
Electromagnetic spectrum starts from Radiowaves, Microwaves, Infra red, Visible light, Ultraviolet rays, X rays and Gamma rays in order of increase in frequency.
Since frequency and wave is inversely proportional. So we can say, above is in the order of decrease in wavelength.
Since Energy and Frequency is directly proportional. So we can say, above is in the order of increase in energy.
Only IR, Visible light and Ultra violet light interacts with eye. ( Optical radiation). So we are concerned about these radiations only regards eye health.
Infra red is near to the Red light region of visible spectrum,hence the name Infra red.
Ulraviolet is near to the Violet light region of visible spectrum, hence the name Ultra violet.
Infra red rays have lesser frequency( higher wavelength) than visible light.
Ultra violet rays have greater frequency( shorter wavelength) than visible light.
From Electromagnetic spectrum, we can understand Infra red ( IR) has less energy than Ultraviloet (UV) rays. But IR is dangerous than UV. Why ?This is because though IR is weak in energy, almost half of the solar energy that reach our atmosphere is in infrared . What it lacks in muscle it make up for numbers !!!.And will your sunscreen or sunglass protect from IR? May be not ! Due to larger wavelengths than UV, they can deeply penetrate in to eye and generate free radicals. The best way to protect from IR is to take antioxidants rich in vitamin C to neutralize free radicals produced by IR.
After Infra Red light, it comes visible light and Ultraviolet light in the order of increasing frequency.
Visible light and Ultraviolet light is also a part of EM spectrum .
Visible light is that part of EM radiation which we could see . Its wavelength is 400-700nm
When a white light ( sunlight) is passed through a prism, it gets diffracted in to different colours- VIOLET, BLUE,GREEN,YELLOW, ORANGE, RED in the order of decrease in energy( increase in wavelength). Since energy of light is directly proportional to frequency, we can say that the above is in the order of decrease in frequency.
Violet light has the highest frequency and highest energy in the region of visible spectrum .
Red light has the lowest frequency and lowest energy in the region of visible spectrum.
The UV rays nearest to the visible spectrum is called UVA( 320-400nm)
The UV rays next to UVA are called UVB ( 280-320nm)
Only 5% of UVB reaches our atmosphere.
Where as 95% of UVA reaches our atmosphere.
The UVA rays have lower energy than UVB . But since they have larger wavelength, they pass through cornea and reach the lens and retina inside the eye. They are not blocked by cornea. This damages the eye.
The UVB rays on the other hand are blocked by cornea . It is also blocked by the window glass of your car, most of the sunglass will block UVB.
But UVA will penetrate deep in to the eyes as it is not blocked by cornea . Only very specific sunglass will block UVA rays. So be careful when you take a buying decision. Ensure it also block UVA.
So for eye care , UVA rays are mostly considered.
Exposure to UVB to some extent is necessary. You can obtain Vitamin D from UVB rays. The food source of Vitamin D is too little so the natural sunlight source is most beneficial. But in places like in seattle, Boston , there is little sun during winter and you cannot obtain sufficient UVB to produce Vitamin D. In that circumstances, you can opt for Vitamin D supplements.
UVB rays when falls on skin ,it activates 7-dehydrocholestrol in our skin and converts it to vitamin D 3. Then in liver it undergoes hydroxylation process and gets converted to 25 Hydroxy Vitamin D (25(OH))- CALCIDIOL. The most accurate method to test the vitamin D is to measure the level of Calcidiol in the Blood. However this is not active form of Vitamin D. In the Kidney it undergoes again hydroxylation process and finally gets converted to 1,25 dihydroxy Vitamin D( 1.25(OH)2 D)-CALCITRIOL. This is the active form of Vitamin D.
UVA has no beneficial use, so you should protect your eyes from these harmful rays.
The Very Harmful wavelength of light is 420-430 nm This is called HEV Blue ( High Intensity Blue light) . They are found in sunlight and also Mobile phones, Computers , TV etc all emit HEV Blue light.This light when reaches the retina, hits the cones in retina. There are 3 cones viz Short wave cone( 420-440nm), Medium wave cone ( 534-555nm) and Long wave cone( 564-580nm).So wavelength of 420 reaching the retina will be completely absorbed.
The energy per photon at 420nm is 2.96 eV
The energy per photon at 700nm is 1.77 eV
The HEV Blue light penetrates the Macular pigment found in the eye.
Low macular pigment can give risk of vision loss ( Age related Macular Degeneration).
Macular pigment absorbs blue light and thereby protects photoreceptors from danger.
So I insist readers to use Sunglass which protects UVA rays and UVB rays with additional protection of wavelengths up to 440nm ( Blue cut )
This article is Dedicated to my beloved parents Late R Uthamakumar Shenoi and Ms Premila who have made me what I am today.
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