I thought I’d continue writing on the rather uplifting theme of summer and talk about another seasonal essential item. No, it’s not flip-flops, although they are definitely a must-have to complete your summer look. Unfortunately this is not a fashion blog, otherwise that’s probably what I’d be writing about. Today I will be exploring the science behind shades. Just deal with it.
Unless you live somewhere like the UK where there is no chance of sunshine any time of the year, you will be very familiar with using sunglasses as a form of protection for your eyes at times when the sun’s rays become too intense. But have you ever stopped to consider how they actually work? Have you ever wondered why there is a such a bewilderingly (is that a word?) large range of choice, with a price tag ranging from a few pounds to several hundred?
You may think that sunglasses are made simply of two pieces of tinted glass or plastic in a plastic or metal frame. As much as this may seem very straightforward, the quality and structure of the lens plays a very significant part in dealing with sunlight. With all the cheap, imposter products around these days, it is important to be able to distinguish between what is real and what is fake.
Electromagnetic radiation can be found with various wavelengths and energies, so is split up into a range of possible frequencies known as the electromagnetic spectrum. Visible light, which is the portion of the electromagnetic spectrum that humans can see, has a wavelength of about 390 – 700 nanometres. As the wavelength of electromagnetic radiation decreases, the energy it transfers increases. Ultraviolet light occupies a portion of the spectrum with a shorter wavelength than visible light, from about 10 – 380 nanometres. Therefore ultraviolet radiation has lots of energy, enough to make substances fluoresce (Let There Be Fluorescent Light…). If exposed to skin over a long period of time, it will cause sunburn and can also increase the chances of skin cancer. It turns out that natural sunlight is very rich in UV light, which is why you should always wear sunscreen when you’re out in the sun (Hello, Summer). Direct exposure to intense sunlight can also damage the cornea and retina inside your eyes, which may lead to long-term ocular problems like cataracts or eye cancer.
There are three types of light that sunglasses will serve to protect against: direct light from the sun to your eyes, reflected light which has bounced off a reflective object (glare), and ambient light which is so scattered that it seemingly has no light source. Sunglasses manufacturers will use a variety of different methods in order to protect against those different types of light which may be harmful or irritating to your eyes. The tinting of sunglasses is essential because it determines the parts of the light spectrum that are absorbed by the lenses. For general usage, red, brown, grey or green are recommended to minimize colour distortion.
Many sunglasses will also have polarised lenses. Polarisation is when the oscillation of waves are aligned into one or more planes of direction. Normal sunlight is unpolarised, vibrating and radiating outwards in all direction. However, when the sunlight is reflected off of a reflective surface such as a lake or a surprisingly shiny road, the light becomes polarized to match the angle of that surface. The reflected glare off the surface is the light that does not make it through the ‘filter’, and it is the reason why you can often not see anything below the surface of a lake, even when the water is very clear. Polarised lenses will be fixed at an angle so that only vertically polarized light can enter, blocking any horizontally polarized light from entering your eyes. Some sunglasses advertised as polarising may be falsely so, but there is a quick test that you can perform to see if the sunglasses really are polarizing. Put the sunglasses on and look at a reflective surface such as a car hood. Slowly turn your head 90 degrees, ignoring the weird looks you get from the people around you. You should notice that the glare from the reflective surface increases significantly.
There are many other less significant techniques used when trying to deal with that pesky sunlight. Mirroring is achieved by applying a coating on the lens that reflects some of the incoming sunlight so that it is not transmitted through the lens. This, despite being useful for bright conditions, does not serve to reflect any of the UV radiation. Lenses can also be made to darken specifically in the presence of UV light, by using a substance that changes shape when exposed, such as silver chloride; these are known as photochromic sunglasses.
Alright, I’ll stop there. You should go outside and enjoy that beautiful sunshine while it still lasts. Just make sure you have the suitable protection. Stay safe and stay cool. Or hot, whatever.