#IonizingElectromagneticRadiation
The Planck-Einstein relation explains and quantify the amount of energy carried by electromagnetic (EM”) radiations (see our article: What is light?). The energy difference between both ends of EM spectrum can be over 1020 times. Physicists found that part of the EM radiation carries sufficient energy to liberate or remove electron(s) from atoms and turn atoms into ions, i.e., ionizing an atom. This can happen to molecules as well. Gamma rays, X-rays, and the higher ultraviolet part of the EM spectrum are generally considered as ionizing EM radiation; the rest of EM radiations in the EM spectrum are considered as non-ionizing EM radiation.
Figure 1: Ionizing and Non-ionizing electromagnetic spectrum
The boundary between ionizing and non-ionizing EM radiation is not clear cut, since different molecules or atoms ionize at different energy levels. In Physics, conventional definition places at the photon energy higher than 12.4eV or at the wavelength lower than 100nm[1]. Ionizing radiation can be categorized into energetic subatomic particles, ions or atoms moving at high speeds (usually above 1% of the speed of light) and the ionizing EM radiation.
Most people should feel a lot of anxiety about the ionizing radiation, as it is commonly-known that it causes cancer or tumor. Although the lasting effects of nuclear weapons used in the World War II took away tens of thousands of lives due to radiation injury, today nearly all radiation cases result from medical or nuclear accidents, for example Fukushima nuclear accident in 2011. Damages done to tissue caused by ionizing radiation are usually far more destructive and longer lasting, although similar injuries to tissues may be caused by strong electrical currents and by some drugs and toxins.
Such kind of radiation-induced ionizations may act directly on the cellular component molecules or indirectly on water molecules, causing water-derived free radicals, i.e., removing electrons from neutral water molecule to produce H2O+. Free radicals are extremely reactive and are strong oxidizing agents, at the molecular level, which destroy biologically active molecules by either removing electrons or removing hydrogen atoms. At the cellular level, it represents the damage of membrane, nucleus, chromosomes, or mitochondria of the cell. The affected cells may turn into or produce malignant cells (i.e., cancer cell) or are inhibited to divide or and at worst, result in cell death.
However, ionizing radiation may not be necessary evil. Exposure to ionizing radiation can also result from irradiation from artificial source, such as medical X-rays/CT Scan instruments or radiation therapy equipment. Such external irradiation can stop when the radiation source is properly shielded.
Figure 2: CT Scan Instrument
Does it mean non-ionizing radiation not being harmful to us?
Most non-ionizing radiation, such as radio waves, microwaves and infrared, is considered harmful only to the extent of the amount of heat energy it transfers to whatever it hits. This is why that microwaves boil water and cook food. Ultraviolet rays are different. Despite of the fact that only part of higher-frequency UV rays are ionizing, the non-ionizing UV radiation have the capacity to cause harmful effects similar to what ionizing radiation can cause, such as an increased risk of cancer due to damage to DNA molecules.
UV radiation denoting EM radiation of wavelength shorter than that of the violet end of the visible light spectrum, having wavelengths between 10 and 400 nm. The shorter the wavelength of the UV ray, the more energy the UV ray carries, the more biological damage it causes. The most common three UV radiation classification is below:
Figure 3: infrared, visible light and ultraviolet spectrum
However, there are other UV radiations, more powerful than UVC, for example, extreme UV, its wavelengths between 10 and 120nm, which is considered as ionizing radiation. There are many subcategory of UV radiation under the ISO Standard ISO-21348[2].
UVC is commonly used to kill micro-organisms, like bacteria and virus, in sanitation system used in hospital or sterilization system in water facilities.
Figure 4: UV Sanitation used in hospital
[1] Lars Persson, On the Boundary between Ionizing and Non-ionizing Radiation, Sweden Radiation Protection Institute, Box 60204, S-10401 Stockhom, Sweden
http://www.irpa.net/irpa8/cdrom/VOL.1/M1_230.PDF
[2] ISO 21348 Definitions of Solar Irradiance Spectral Categories (Courtesy of Space Environment Technologies spacenvironment@spacenvironment.net, http:SpaceWx.com)
http://www.spacewx.com/pdf/SET_21348_2004.pdf
]]>In physics, light is the smallest quantity of energy that can be transported. A photon, an elementary particle without a real size, cannot be split, only created or destroyed. Light also has a wave-particle duality, being kind of particle and a wave at the same time. However, in ordinary usages, when we say light, we actually mean visible light, which is a very tiny part of the electromagnetic (“EM”) spectrum, that are the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes. Radio waves that come from a radio station is another type of EM radiation. All types of such electromagnetic radiation travel 299,792,458 meters per second in a vacuum, also known as the speed of light (commonly denoted as “c”).
What is EM radiation?
Electromagnetic radiation includes an enormous range of wavelengths and frequencies and carries different level of energy. The EM spectrum is generally divided into eight regions, in order of decreasing wavelength and increasing energy and frequency, they are commonly named:
Gamma rays have the smallest wavelength because they are the highest energy photons; radio wave have the largest wavelength because they are the lowest energy photons. How many energy difference among the ends of the electromagnetic spectrum? Electron-volt, or eV, is a unit of energy in physics, widely used in solid state, atomic, nuclear and particle physics. In astronomy, it is widely used to describe the energy level of light or EM radiations.
Figure 1: Electromagnetic Spectrum
The Planck-Einstein relation (E = hf, where h is known as Planck’s constant) connects the particulate photon energy (E) with its associated wave length (f). As mentioned above, all types of EM wave are at the same speed of c. Therefore, the particulate photon energy has an inversed relationship with its associated wavelength. Now, let us take radio wave and gamma rays as examples. The biggest long wavelength of radio wave can span from 10,000,000m to 100,000,000m. Most gamma rays are under 10 picometers (denoted as “pm”, one picometer is 1 x 10-12, i.e. 1/1000 of nanometer), which is far smaller than a hydrogen atom. By applying the Planck-Einstein relationship, we can depict a huge energy difference between very long wavelength radio waves and gamma rays i.e., of 1020 (hundred million trillion or hundred quintillion) times!
What is visible light?
What makes visible light special? Um…our eyes make them special. Human eyes are also evolved to capture visible light which carries the information around us. However, not all animal eyes were evolved in the same way, for example, bird eyes can recognize ultraviolet rays which is generally invisible by human eyes. Furthermore, bug eyes like bee eyes can recognize ultraviolet rays as well.
Visible light is not white. A beam of white light will be dispersed into a visible light spectrum as below. Rainbow is a natural phenomenon happened after raining.
Figure 2: Dispersion of white light through a prism
Figure 3: Rainbow after a rainy day
Such visible light spectrum are EM radiations of wavelength from 380 to 750 nanometers.
Figure 4: Visible light spectrum
By applying the Planck-Einstein relationship, we know that gamma rays is 100,000 times powerful than the visible lights.
In short, light includes all electromagnetic radiations travelling at the speed of light, c, in vacuum. All those electromagnetic radiations form a continuous electromagnetic spectrum. Light, in our ordinary use, generally refers to visible light, which is just a tiny part of electromagnetic spectrum. As a matter of fact, solar light from the Sun includes not only the visible light but also other electromagnetic spectrum, like ultraviolet rays. Even the artificial light sources emitting electromagnetic radiations other than visible light, for example, tanning lamp emits the ultraviolet rays which make our skin tanning. However, as we explained above, some of the electromagnetic radiations are much more powerful than visible light, and we should avoid exposing in those high energy electromagnetic radiations.
]]>We suggest the way how to clean the sunglasses in another article. You may read with the below link:
In this article, we focus on how to keep the sunglasses from breakage.
Using a protective case
Get into the habit of putting your sunglasses in a protective case or holder whenever they are not on your face. Use the protective case to store your sunglasses, as the lenses can easily get scratched if you fail to keep them somewhere safe. A protective case may keep your sunglasses away from many kinds of damage, including lens scratches or temple breakage incurred while your sunglasses bounce around in your handbags.
Make sure that the protective case is clean and dust-free, as any abrasive particles inside the case may cause the lens scratched. Therefore, wrap your sunglasses up with a clean microfiber cloth when placing them in a solid protective case.
But, if you don’t like a bulky case, find a sleeker one. Microfiber pouches are also great to keep the sunglasses at the glovebox or glove compartment in your car.
Place your sunglasses carefully
Never place your sunglasses on a desk, counter, bar table or automobile dashboard, as small movement on any hard and rough surfaces may cause lens scratches.
Don’t put sunglasses on the top of your head. One of the common reasons for sunglasses breakage or lens scratches is because they fall off from the head. Besides, putting them on the head can distort the shape and shorten their lifespan.
Butts are the enemies of sunglasses or eyeglasses, as another common reasons for sunglasses breakage is sitting down on the top of the sunglasses. Many people leave their sunglasses on a car seat for a few minutes, when they get back to the car and they find the butts hit the sunglasses. So, look before you sit.
Besides, never leave your sunglasses in your automobiles for too long, as cars amplify extreme temperatures. In a hot summer, car temperatures can reach upwards to 90 degrees Celsius. Temperatures of over 80 degrees Celsius can damage even the toughest lenses, frames or plastic temples. In particular, plastic lenses should not be exposed to high temperatures, which could have an adverse effect on the durability of lens coatings. Mirror or anti-reflective coatings on the lenses can be damaged. In some extreme conditions, such as a car in desert, the extreme temperature fluctuation magnifying in the car can lead to surface cracks due to the different structures of the base lens and the lens coating. Therefore, never leave your sunglasses in the car for long periods of time. In fact, you should enjoy the sunshine with your sunglasses!
Use two hands
Like give your loved a hug with both hands, put on your sunglasses with both hands. This keeps the sunglasses straight and in the right alignment. Similarly, take them off with your both hands, as taking them off one-handed stretches them out and makes the hinge loose, even the sunglasses are of spring hinges. Love your sunglasses, use both hands and let your sunglasses stay right all summer long!
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Sense is a method of perception, helping us to get information about what is going on around us. Human has five senses: taste, sight, touch, smell and sounding. Human eye is an amazing organ which reacts to light and gives us sense of sight. Eyes capture light and transform it into electrical impulses to our brain and let us interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. However, not eyes of all creatures evolved and structured in the same way, for example, human vision is different from bird vision or bug vision.
Figure 1: Eye Structure of a Human Eye
As you can see from Fig 1, light first pass though and is refracted by the cornea, the transparent front of the eye. Refracted light enters the pupil, an adjustable hole controlled by iris, and is then focused on the retina by the lens. Light-sensitive nerve cells in the retina like rods (for brightness) and cones (for color) react to the light and turn light into electrical signals to our brain. They interact with each other and send messages to the brain. The rods and cones enable vision.
With two eyes, our brain receives two slightly different light signals from different angles. The brain combines these two images into a three dimensional image, telling us how something is far away. We called it depth perception.
Cornea is the clear and transparent front part of our eye. Most of us know it refract light and contributes most of the focusing power of our eyes. Astigmatism usually is caused by an irregularly shaped Cornea, which forms multiple focuses on the retina, resulting in blurred or distorted vision. We called it corneal astigmatism. Squinting is the most common symptom of astigmatism, as people squint to see better.
Another function of Cornea is UV filter of our eyes. It absorbs ultraviolet (“UV”) radiation and protect the internal part of eye structure, such as retina. Studies found that the corneal layers absorb the UV rays from 240-400 nm and being important in preventing damage of our internal eye structure by UVB[1].
Even though cornea protects the internal eye structure from UV radiation, it can be damaged easily by over-exposure to the UV radiation from the sun or from other sources of UV light, such as tanning lamp, flash light. Such damage to cornea can be considered as the sunburn of cornea. It makes our eyes in pain, at worst loss of vision.
Figure 2: Pupil and Iris
The pupil is the small black hole in the center of the iris of the eye that allows light to reach retina. It looks like a black hole or spot in our eyes, because light, passing through the pupil, is eventually absorbed and turned into electrical signal by the retina. Human pupil is circular-shaped, but some animals have vertical pupils, whereas others have horizontal. An interesting study found that the pupil shape may relate to the foraging mode of the animals. For example, herbivorous animals are very likely to have horizontal pupils and ambush animals have vertical pupils[2].
Take camera as an analogy, the relationship between pupil and iris just like the aperture and aperture stop. The iris changes the size of the pupil to let more or less light in to prevent damage to the eyes by over-dosage of light. The pupil gets wider in the dark but narrower in the bright. Normally, the size of the pupil is controlled by the iris automatically in response to the brightness of the environment. However, medical provider may us special eye drops to make your pupil dilating (i.e., being wider) for examination of retina, as only a limited view can be observed through an undilated pupil. An eye protection is normally required after such eye examination in order to prevent over-exposure of light to the eyes.
The lens is another transparent structure in the eye, apart from the cornea. It is located behind the pupil and suspended by the ciliary muscles surrounding the lens. The ciliary muscles change the curvature of the lens, just like the iris adjust the size of pupil. The adjustment of curvature of the lens is called accommodation. Accommodation enable us to maintain a clear image on an object as its distance change, for a running object. Cornea and lens are responsible for the optical power of our eye. A diopter, a unit of measurement of the optical power of a curved mirror or lens, is equal to the reciprocal of the focal length in meter, in short, it is a unit of reciprocal length. The young men normally have the best vision, approximately 15 diopters, i.e., 1/15 and can change focus from the distant to as near as less than 6.6 cm (i.e., 1/15 meter). Accommodation, the focal power of the eyes, declines dramatically with age, and most of people have approximately less than 2 diopters at the age of 45 to 50 years. Accommodation decreases to about 1 diopter by the time a person reaches 70 years[3].
The natural crystalline lens of the eye may not be perfectly symmetrical front and back, such mis-shaped lens can lead to astigmatism. This is called lenticular astigmatism, which is different from the more common corneal astigmatism.
Similar to cornea, lens of the eye is also responsible to filter UV radiations in the wavelength between 300 to 400 nm, i.e., mainly UVA and protect the retina away from such UV radiations. Although lens of the eye absorb UV rays, UV rays would contribute to the cause of Cataract, which is a clouding that develops in the crystalline lens, obstructs the passage of light and leads to a decrease in vision. Surgical operation to remove the cloudy lens and replace it with an artificial lens is the only way to get rid of cataract. Cataract is generally considered as aging-associated diseases, but studies shown how UV rays may contribute to cataract[4]. Prevention is better than cure - wearing UV blocking sunglasses to keep eyes away from harmful UV rays. Cataract also happens to other mammals, like dogs.
Figure 3: The Old Chihuahua with Cataract
Retina is display used in many products of Apple, like iPhone, iPad, iPad Pro, Macbook Air, Macbook pro and iMac. Haha...ha, it is not the retina we are referring to. The retina of the eye is a very thin layer of tissue in which consists of our photosensitive cells and optical nerve cells. Photosensitive cells in the retina is to receive light that the lens has focused, convert the light into electrical neural signals by the optical nerve cells, and send these signals to the brain for visual recognition.
Rods and Cones
Photosensitive cells in the retina allow are light sensitive cells, responsible for detecting qualities of light such as color and light intensity. Two types of photosensitive cells in our eyes help us to differentiate colors and capture light in various light intensity conditions: cones and rods. In adult human eyes, the entire retina contains about 6 million cones and 120 million rods. Cones provide us with color vision, but they require relatively more light in order to generate signals. Humans have three different types of cone cell, which react to different wavelengths of visible light and generate three different and distinct signals. They are S-Cone, M-Cone and L-Cone, which react to light of short wavelengths (i.e., S-Cone response to blue), medium wavelengths (i.e., M-Cone responses to green), and long wavelengths (i.e., L-Cone responses to red). Therefore, we said humans have trichromatic vision. Color blindness occurs when one or more of the cone types are faulty. The rods are narrower than the cones and distributed differently across the retina. Unlike cones, rods are extremely sensitive to light. At a very dim-light environment, our vision is based solely on the rods. The faulty of rods cause to night blindness.
Other animals may view differently from us, as they have more Photosensitive cells in their retina. Some birds have four types of cones rather than the three we have. The additional cone cell of birds reacts to ultraviolet, which is invisible to humans. The exact number of cones varies in each bird species but is typically higher than humans. These explains why bird is considered to have a better vision than us.
Due to the retina's vital role in converting light into biological neural signal, damage to it can cause permanent vision loss, retinal detachment, where the retina is abnormally pulls away from its normal position, can separate the retinal cells from the layer of blood vessels that transport oxygen and nourishment to the retina. It is a very emergency situation, the longer the retina detached from the blood vessel layer, the greater the risk of permanent vision loss of the affected eye.
Reference:
[1] Lajos Kolozsvári, Antal Nógrádi, Béla Hopp, Zsolt Bor; UV Absorbance of the Human Cornea in the 240- to 400-nm Range. Invest. Ophthalmol. Vis. Sci. 2002;43(7):2165-2168.
http://iovs.arvojournals.org/article.aspx?articleid=2123733
[2] Martin S. Banks, William W. Sprague, Jürgen Schmoll, Jared A. Q. Parnell and Gordon D. Love, Why do animal eyes have pupils of different shapes?
Science Advances 07 Aug 2015: Vol. 1, no. 7, e1500391 DOI:10.1126/sciadv.1500391.
http://advances.sciencemag.org/content/1/7/e1500391.full
[3] Duane A: Studies in monocular and binocolar accommodation with their clinical applications. Am J Ophthalmol 5:865, 1922.
[4] https://nei.nih.gov/news/briefs/uv_cataract
(Courtesy: National Eye Institute, National Institutes of Health (NEI/NIH))
About the lens coatings
Most of the lenses of sunglasses are with coatings, like mirror coating, scratch-resistant coating, anti-fog coating and UV-blocking coating. The scratches you seen may not be on the surface of lenses but on the lens coatings, therefore, we should avoid any possible damage on the lens coatings while cleaning the sunglasses. Most lens coatings are using a method called Chemical Vapor Deposition to apply various thin films of minerals onto the lens. What the film is really depends on the chemical formula used by the lens manufacturers. Aluminum, silver or even gold may be used for the mirror coating of lens, and aluminum is the most commonly used one, as it is cheapest. Any substances which reacts with the aluminum may cause a permanent damage on the mirror coating of the sunglasses. In order to keep the lens of your sunglasses scratch-free as long as possible, you should carefully protect such thin layer of lens coatings.
Most common way to clean the lenses of sunglasses
Many people clean the lenses of their sunglasses, by breathing warm, damp air on your lenses and gently wiping the fog off with a paper towel, shirt, jumper or handkerchief. Later, the plastic lenses got scratches on its surface after times of such cleaning processes. Shirts, jumpers or handkerchiefs may have sand, dirt or similar abrasive particles which will scratch the lens of your sunglasses or wear off its coatings. Wood tissue of the paper towel may be hard enough to cause scratches. You may then order a new pair of sunglasses in less than a year. Some of you may be looking for the way to clean your sunglasses with scratching it.
Our suggested approach to clean your sunglasses
The best way we are recommended it to wash your sunglasses with cold or lukewarm water and mild hand soaps (not Palmolive or Dawn) or baby soaps and dry your sunglasses thoroughly with a clean microfiber cloth. This method is not new and many people clean their sunglasses in the same way. However, here are something you should avoid.
Once you learn how to clean your sunglasses, but how often you should clean your sunglasses --- the time between cleanings depends on whether you have a need to clean it. Surely, you should clean it when they are so dirty or greasy that you cannot see clearly. After you clean in properly, place it in a protective case and keep it away from extreme temperature and dusts.
However, you must clean it after each time of outdoor activities, especially, water sports. Sea water contains salt. If you don’t wash your sunglasses after water sports in the beach, either traces of salt or sand particles may be on the surfaces of lens on the both sides. And you may scratch your lens when you try to remove by rubbing the lens even with a clean microfiber cloth. Why? Imagine if there are sand on your lens, and rubbing the lens with microfiber cloth just cause the sand slide on the lens and cause scratches. In addition, sea water can cause rusting on the metal parts of your sunglasses, like the metal spring hinges. What if after games in swimming pool? Water in the swimming pools is sanitated with chemical compounds, in order to ensure the hygiene in swimming pools. The chloride-based compounds are commonly used, which may react with the lens coatings. Therefore, wash your sunglasses with lukewarm tap water to remove the sand or sea water right after having water sports or even just enjoy your sunshine in the swimming pool or on the beach.
The above tips may apply for cleaning your eyeglasses as well.
Washing your sunglasses with ultrasonic cleaner
If your sunglasses has not been cleaned for a period of time and greases and dirt built up on the nose pieces and other components of the frame, it may become impossible to keep clean. Then you may need to ask assistance from your local eye care professional. Sometimes, sunglasses can be cleaned more thoroughly with an ultrasonic cleaning machine and the yellowish silicon nose pieces can be replaced with new crystal clear ones.
However, if you have an ultrasonic cleaner at home and want to wash or clean your sunglasses with it, please do it carefully. Don’t use any strong cleaning agent, except for one to two drops of mild hand soaps. Don’t you hot water, even the user manuals of ultrasonic cleaner suggest it. Don’t sunk your sunglasses in the ultrasonic cleaner too long (less than three minutes). A real ultrasonic cleaner is very powerful, it can make a tin foil or aluminum household foil with hundreds of hole within 30 minutes. Remember most of mirror coatings of sunglasses are made of aluminum. Google tin foil test for ultrasonic cleaner and you will see why.
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