TLDR summary: No harm using it, but it's not just about protecting against your phone and computer screens.
[ Note: With new products in the market, we have edited this post as well as split part of this post into another article about UV420 lenses which we will post soon. We hope this gives better clarity. ] - 14 Oct 2017
UV LIGHT, BLUE LIGHT, AND THE EYE
We first need to understand UV light, the often talked about 'blue light', and how they affect the eye.
The visible light that you see is made up of light across the entire spectrum from red to violet (the rainbow colours, remember your primary school science?). On one end, red light has a wavelength of about 700nm, while on the other end, violet light has wavelength of about 400nm. Beyond that violet light is ultraviolet, which has an even shorter wavelength - 400nm to 10nm.
|(CC BY-SA 3.0)(Image source and author information)|
Now here's the gist - the shorter the wavelength, the more energy there is. Which is why ultraviolet (UV) does so much harm to our skin and eyes, and for that same reason, why there is an entire product line to protect against UV rays - sun-block lotions and UV-blocking lenses.
Side note: Have you ever seen stickers on sunglasses stating "UV380" or "UV400"? Yup - that number is basically the wavelength.
The multi-coated lenses that comes with your glasses would also have UV protection - some stop at 380nm, while others block up to 400nm. We guess this may not be absolute numbers and so there will be room for error: for instance lenses that block up to 390nm may be labelled as 380nm anyway, or maybe a lens labelled as 400nm may block 99% of UV at 380nm but block 95% of UV at 400nm. Some lenses are simply labelled "UV400-UV380" or "UV-A".
Then came lenses that blocked transmission up to 420nm, often known as "UV420 lenses", although technically UV stops at 400nm. This is sometimes demonstrated using a laser pointer (with a 405nm wavelength, if your're curious) at local optical shops. We will explore this in another post.
The popular "blue-light lenses", also known as "PC lenses" (not to be confused with lenses made of PolyCarbonate material) or "computer lenses" (not to be confused with a prescription given for computer and intermediate use), actually reduce the amount of blue-violet light that allowed through the lenses.
This article shall talk about the "blue-light lenses". For the post about UV420 lenses, click here.
Now to the topic of blue-light blocking lenses. First, it is good to point out that the blue-light blocking lenses actually reduce the amount of blue-light passing through the lenses, but not cut off blue light totally - if we were to remove blue totally, colours would look quite wrong!
While we may mention "blue-light blocking" in this article, do note that these lenses actually reduce, not totally cut off the entire blue part of the spectrum! Also, different brands or even batches of lenses could be different from each other.
DOES IT WORK?
Do these lenses protect you from blue light? Well, the simple answer is yes.
The very widespread way of marketing such lenses is that it protects you from digital devices like your mobile phone and computer screen.
But the doubt still remains as to how significant the blue light from your mobile phone or computer screen is, considering that blue light as everywhere - our dear sun is a great source of it! Will the blue-light from your phone be able to cause or significantly add to eye damage? That is not easy to prove. Or disprove.
Clearly if we want to go down this "everything must protect until 100%" then we would probably have to put on long-sleeve shirts before sitting under a light bulb. And while we're at that, why not sleep in a chamber with air filtered through a HEPA filter? Don't forget the blocks of lead to reduce radiation exposure!
There appears to be an understanding that you should get these lenses because they protect against the mysterious rays coming out of a computer screen or mobile phone screen which are, alas, going to screw up your eyes if you don't fork out the extra $100 to upgrade!
|Bluish-violet reflection of the lens|
THE LESSER-KNOWN USES
I can't prove or disprove the theory that your eyes are going to spoil from not upgrading to blue-light blocking lenses. But there are other great uses for such lenses, actually! And they don't exactly have to do with protecting your eyes from the mobile phone.
1) Night-time vision
At low illumination levels (like when you're out at night), we experience more glare because our pupils dilate to allow more light in. Also, the Purkinje effect sets in, which means your eyes become more sensitive to the blue end of the colour spectrum. Since the different colours that make up the light refracts differently through the parts of our eyes, and blue light scatters more, reducing the amount of blue light may help in making things look sharper.
2) Circadian rhythms
Blue light also helps in telling our bodies if it's daytime or snooze time - so there is a possiblity that the use of artificial lighting at night can trick our bodies into thinking it's daytime, hence affecting our sleep-wake cycle. Reducing blue light, then, may solve the problem.
3) Reduced chromatic aberration (CA)
Since CA is the defocus or spreading out of the visible light we see into the different colours, people who tend to see fringing of colours (e.g. purple fringes around an object's or image's edges) could benefit from these lenses, since they reduce part of the light spectrum, leaving behind lesser colours to scatter. Hence this may be a possible use for the lenses too!
ARE THERE DISADVANTAGES?
Yes - when you reduce the blue-violet spectrum of light, what you see becomes a 'warmer' colour, much like moving your camera's white balance setting from 'daylight' to 'cloudy'. Eventually we adapt to it and we don't take notice of it. But if you work closely with colours, say in the photo-editing or printing industry, then this could alter your perception of the colours (not a problem if it's a specific pantone colour the customer wants though).
To get an idea - see the pictures at the end of this post.
SHOULD YOU GET BLUE-LIGHT BLOCKING LENSES?
While there isn't a compelling reason to go out and get these lenses right at this very moment, they do give quite a number of benefits so it's one more option for your when you get your next pair of glasses. Hopefully the information provided here has helped you to make an informed decision.
You may also want to read about the UV420 lenses.
If you want to get a pair of these blue-light blocking lenses, there's a top-up option on our no-frills Frame+Lenses package, or if you prefer the branded ones, we have these brands available:
- Crizal Prevencia
- Hoya BlueControl
- Pentax INC Blue
- Zeiss BlueProtect
They come in both single vision, as well as progressives (multifocal) lenses, and in different indices too (high index, etc.). To find out more, visit us - 194 Kim Keat Ave, Toa Payoh - we will give you what suits you best.
These are photogaphs taken with an actual blue-light blocking lens over the camera. The white balance is fixed for both the 'with' and 'without' shots hence the camera does not compensate for the shift in white balance with the lenses.
|without and with blue-light blocking lenses - outdoors|
|without and with blue-light blocking lenses - reading|