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More information about Blue-Violet Light Blocking Lenses

Somehow found this article? We encourage you to to read our "Are Blue-Light Lenses a Myth" first.

Otago Optical - Electromagnetic Spectrum
Electromagnetic Spectrum

The Electromagnetic Spectrum

If you've paid attention in physics class, the EM Spectrum should look familiar. Visible light extends from Red to Violet - the rainbow colours, ROYGBIV as it is often taught.

Beyond red is infra-red, and beyond violet is ultra-violet. Some remote controls use infra-red to communicate with the host devices, while we all know the harmful effects of ultra-violet.

Ultra-violet can cause changes to our skin - such as when we stand under the sun without sun-block and get sun burnt. It can also (as a risk factor) cause cataracts and macular degeneration.


Ionizing and Non-Ionizing Radiation

The "US Federal Communications Commission material defines ionizing radiation as that with a photon energy greater than 10 eV (equivalent to a far ultraviolet wavelength of 124 nanometers)" - Wiki

"Near ultraviolet, visible light, infrared, microwave, radio waves, and low-frequency radio frequency (longwave) are all examples of non-ionizing radiation" - Wiki

Ionizing radiation can be a health hazard, and as can be seen, towards the gamma-rays side of the EM Spectrum, is ionizing radiation, and vice versa. This shows the higher photon energy at lower wavelengths (towards the left side of the EM Spectrum drawing above).


Photon Energy

We can clearly see the highest photon energy levels at the violet colour, and decreasing all the way to red colour.


The low-down on Why We Want To Block Violet

As we can see above, violet light has higher energy than the other colours, although you don't have to hide in a lead chamber, because it isn't ionizing radiation (like gamma rays from a nuclear bomb is).

But since it has higher energy, there may be more potential to cause effects which may be harmful.

Of course, these effects may be cumulative, i.e. added on over a period of time, or dependent on the intensity of the violet light.

This has been supported by studies:

"Blue-violet wavelengths lie close to UV light and therefore have higher energy (being inversely proportional to the wavelength). An excess of blue-violet is considered to be hazardous to the human retina if exposed for a long period of time as it radiates more energy than blue-turquoise and other visible light." - Sapkota, R., Pardhan, S. (2016)

"400 nm light radiation can cause significant dose-dependent decreases in RPE cell viability as well as degradations of DNA/RNA and mitochondria in RPE cells, while 420 and 435.8 nm light radiation cause no cellular damage." - Youn H.Y., Chou B.R,. Cullen A.P., Sivak J.G. (2009)

"Eyes of anesthetized rats and mice that did or did not contain rhodopsin were exposed to green (550 +/- 10 nm) or deep blue (403 +/- 10 nm) light for up to 2 hours. Exposure to blue light resulted in severe retinal damage and activation of the transcription factor AP-1 in rats. In contrast, green light had no effect." - Grimm, C., Wenzel, A., Williams, T., Rol, P., Hafezi, F., Remé, C. (2001)

You will realise that in the third study listed there, "blue light" is used to refer to 403nm light, which is, of course, violet light. This shows that sometimes, the terms "violet" and "blue" are used interchangeably. This could be one of the reasons why some shops advertise "blue-light blocking lenses" but are actually using "violet-light blocking lenses".

As we have noted in our other article (Are Blue-Light Lenses a Myth), "some stores may (perhaps inadvertently) advertise blue-light blocking lenses, but actually be using these violet-light blocking lenses instead".


The Laser Demonstration and Lens Variations

Using a laser pen-light, shops are able to demonstrate if a lens blocks violet light. For most of these pen-lights, the bulb is rated to emit at a peak of 405nm - violet light. However, since these aren't precise laboratory equipment calibrated to official standards, there can be variations.

Also, we would expect that while the emission (un-exactly) peaks at 405nm, it does not mean that there is zero emission at 404nm or 406nm.

The illumination or power levels can also be different, i.e. one pen-light could be brighter than another.

Since the lenses are rated to 420nm (again, probably not super accurately), if there is light emission from the pen-light beyond 420nm, it will go through the lens.


Furthermore, lenses themselves can also have variations, depending on the lens thickness, type, index, manufacturer, batch, storage, and so on. While the lenses are rated for 420nm, it probably doesn't block 100% at 420nm, and block 0% at 421nm. Perhaps it allows 15% transmission at 420nm, and 5% transmission at 410nm? Who knows - unless we run the individual lens under a lab test.

This can cause a greater difference when one pair of glasses is tested against another, especially if the back surface is white or has optical whiteners (e.g. printing paper). A small amount of violet-light going through would result in what seems to be a large amount of reflection off the white surface.

This can be disconcerting for some consumers who have "absolute" expectations.

To conclude, one pen-light's laser may "shine through" a lens more than another pen-light's laser, and the same with lenses - one lens may allow more light through than another. This is a normal and accepted phenomenon in the industry, not sus.


Should you get these lenses?

If you're concerned and prefer the latest in technology/protection, why not? We suggest these lenses can be used as an every-day lens, whether you spend more time outdoors or in front of the computer or mobile. If budget is a concern, one can definitely also make do without these lenses, as long as the standard lenses provide ultraviolet (UV) protection.

Our package glasses already include multicoated lenses with UV protection - at no extra charge.

Violet-light blocking lenses are available as a top-up option - for the latest prices, please refer to our in-store displays. Our prices and pricing system is always transparent, and we update prices and products regularly in order to provide the best value to you, our customers.


Do these lenses feel different?

If you've gotten a lens with a blue coating, you may have realised a yellowish-tint to the lenses. We do see wearers of such lenses eventually prefer standard multicoated UV-blocking lenses.

For violet-light blocking lenses, at this moment we find that it is well-tolerated by wearers, even though technically it makes things look more "greenish". It may be due to us being less sensitive to violet light (as compared to blue), and that we are blocking the part of the violet closest to ultra-violet rather than the entire violet spectrum (no "block 80% blue light" sold here, sorry not sorry).

If you are concerned, why not give it a physical look before committing to whether you want these lenses?

Note: We may update this article in the future as more research is published and as the consensus and understanding towards this topic changes.


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