There's a lot of interest at the moment in blue light and how it affects us. Particularly interesting is whether the light given off by computer screens, smartphones and televisions, used late at night, could be fooling our brains into thinking it's still daytime and stopping our natural slowdown into bed and sleep. If you're laying awake at night, blue light could be contributing. Irritated eyes? Headaches? It could be blue light.

The rise of smartphones and tablet computers is said to be part of the problem, but it's not the whole story. To really understand, we need to get a little technical.

So what is blue light?

Light reverberates with a frequency, like a radio frequency. We perceive different frequencies in the visible range as different colours. A wavelength is the distance from peak to peak of that wave. X-Rays, UV, visible light, microwaves and radio waves are all the same thing, just with different wavelengths. X-Rays have extremely small wavelengths, while radio waves can have very long wavelengths of a kilometer or more.

Visible blue light tails off into ultraviolet light (UV) at the extreme end of our ability to perceive light. UV is categorised into three types.

  1. UVC is light with a wavelength of between 279 & 200nm (nanometers, a millionth of a millimeter). We needn't worry too much about this as it's filtered out by the ozone layer. It is used to sterilise, for instance in dentistry.
  2. UVB light has a wavelength of between 314 & 280nm. It gives you sunburn, and it is implicated in skin cancer, cataracts and the degeneration of retinal tissue.
  3. UVA has a wavelength between 380 & 315nm and is the sort of UV you might encounter in a nightclub or tanning salon.

Finally we have 'blue light', near UV, which is light between 381 & 500nm in wavelength. About 25-30% of sunlight is 'blue light'.

The UV index provided by the weather forecast is designed to let you know the risk of sunburn, so it concentrates on UVB. Stratospheric ozone loss has led to the penetration of more UVB over the last few decades. Just in case you were thinking of it, don't go above 4,500m high in Bolivia where a UV index of 43.3 has been reported (11 is 'extreme risk', the highest in Scarborough has been about 8.2, however remember that UV intensity can double if you are near reflective surfaces such as water, sand or concrete).

So blue light exists in nature, we've adapted to it so there's nothing to worry about, right?

We are adapted to 'normal' sunlight, of course. The problem is that UV damage is cumulative over your lifetime, and we are living longer. To live longer without increasing the risk of UV damage to our eyes, we need to protect them.

There are a couple of points to make here. Most of the UV your retina will receive during your life is received before age 20, after that the eye lens becomes a natural absorber of light wavelengths between 400 & 320nm (a little 'blue light' and most UVA). This helps to make a case now for giving children UV eye protection. New PNX lenses can filter 100% of the UV and aren't expensive. Also that UV energy, absorbed by the lens of the eye, can contribute to cataracts, so you need UV protection as an adult too. UV is thought to be a contributory factor to macular degeneration (as well as cataracts, skin ageing, immunosuppression, DNA damage and skin cancer).

But let's get back to blue light. Fluorescent tube lighting produces blue light. How fluorescent tubes work is: electricity excites mercury vapour that produces UVC at 254nm, and that light excites a phosphor coating on the inside of the glass that re-emits visible light. Any UVC that isn't absorbed by the phosphor is absorbed by the glass. No problem. But mercury also emits at 365nm (UVA), and that may not be absorbed by the phosphorus and most will pass out into the environment. If you have fluorescent lights at work, you will be getting nearly 14% of your UVA exposure from that alone.

The nub of the blue light problem for optometrists, though, is backlit LED screens (if you can still see your screen at night with the room lights off, it's backlit). The light from those peaks at 460nm (blue light). (Backlit screens emit 3.2 times more blue light than non-backlit screens.) Humans have a novel, non-visual, short-wavelength-sensitive photoreceptor system that drives and resets our circadian pacemaker. In simple terms: we have a specialist blue light sensor that tells our body when it's daytime and when it's night-time. It drives melatonin production, alertness, performance, and raises or lowers brain activation. As we get closer to bed-time, we really want that system to calm us down and edge us towards sleep. Contrarily, blue light shouts daytime! Screen light can tell our brains to stay awake and alert, and our circadian clock can get confused.

So what can we do about blue light? In simple terms, don't use a screen (computer, TV, smartphone, tablet) late in the evening (which is when most people want to use one).

If that seems unreasonable, pop in and talk to us about solutions. Blue Control, a spectacle lens coating, is especially formulated to stop blue light so you can carry on enjoying late night films or social media without interfering with your sleep.

There's another benefit of Blue Control that you might like. White light is composed of a mixture of coloured light. Each colour requires our lens to be set slightly differently for clear focus. That means our eyes are constantly judging the best possible average focus point depending partly on the colour composition of the scene you are looking at. By removing blue light, Blue Control reduces the range of values our eyes are trying to focus for, making focusing easier. The result: clearer sight and less eye strain (athletes wear Blue Control for extra clarity and performance).

http://www.cclvi.org/contributions/effects1.htm
http://www.revoptom.com/continuing_education/tabviewtest/lessonid/109744/
http://uk-air.defra.gov.uk/data/uv-data
http://journal.frontiersin.org/Journal/10.3389/fenvs.2014.00019/full
http://montreal-protocol.org/Meeting_Documents/research-mgrs/8orm/Cook_U...
http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/Understand...
http://en.wikipedia.org/wiki/Ultraviolet_index
http://www.ncbi.nlm.nih.gov/pubmed/21415172
http://jap.physiology.org/content/110/5/1432
http://www.dvice.com/2013-8-7/study-hints-depression-link-blue-computer-...
http://www.revoptom.com/continuing_education/tabviewtest/lessonid/109744/
http://www.webexhibits.org/causesofcolor/1.html
http://en.wikipedia.org/wiki/Ultraviolet