How Do Sun Glasses Work?
Those who live in the tropics probably all wear sun-glasses. It also amazing that how little we think about them, except for the fact whether they make us look smart or not. In any typical shop dealing with sunglasses there is a huge variety to choose from. There are differences in the tint, and then there are photo chromic and polarizing sunglasses. Their sizes also vary.
A pair of sunglasses doesn’t seem like a complex machine – it has got two pieces of tinted glass/plastic in some sort of a plastic/metal frame. It turns out that just two pieces of glasses can be combined in a variety of ways and each of those combinations can have a big effect. A good pair of sunglasses should: provide protection from UV rays, intense lights, glare and must not let light of certain frequencies of light to pass through them. Sunglasses can be thought of as instruments which modify incoming light to match it to our eyes. And different lenses use different ways to do the job.
A quick look at what light is will help us easily understand how sunglasses function. Light is an electromagnetic wave and it carries energy. Light that falls in the wavelength of 400 – 700 micrometers helps us see the world around us because our eyes are sensitive only to this narrow band of electromagnetic spectrum. UV rays are also electromagnetic waves but they have got more energy than the visible light and exposure to UV rays can damage the retina of an eye. What sunglasses do is: they eliminate UV rays from the spectrum of the light and bring their intensity down to the levels, where they are more tolerable.
Sunglasses use following technologies to keep our eyes safer:
(1) Tinting:
The kind of tinting (its color) determines which part of the light spectrum will be absorbed by the lenses i.e. waves of which particular wavelength will be absorbed.
(2) Polarization:
The light vibrates in three dimensions but polarizing substances modify light and make it a two-dimensional wave, thus lessening its energy.
(3) Photo chromatic lenses
Ever wonder why some sunglasses change color in the sun. That is because of the photo chromatic lenses fitted in them. The lenses have molecules of silver chloride or silver halide embedded in them. This substance is transparent to the visible light but when exposed to UV rays, they undergo a process and their relative positions are altered. The new structure, in addition to absorbing UV rays, also absorbs a portion of the visible light causing it to blacken. The reaction is reversible, so once we are back indoors the color changes again.
(4) Mirroring
This technique includes polishing the visible part of the glasses with a special substance with reflects colors. They are also called ‘half-silvered’ mirrors and let only half of the light falling on them to get through.
(5) Anti-reflective/ UV coating
Anti-reflective coating is applied on the side of glasses which faces our eyes. The reason behind this coating is: light that strikes the inner surface after reflection may harm our eyes and the coating prevents that from happening.
The function of UV coating is to eliminate UV radiation.
This is the basic science behind how things work. The quality of a lens may also depend upon how a person uses his sunglasses i.e. whether he cares about them or not and their size and a lot of other human factors.
Category: Technology