The power of light to change your world for good
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For your eyes only

You’re probably reading this on a computer, catching up on social media after hours. You’re not alone. Europeans spent two to three hours in front of a screen per day outside of working hours – Time spent watching TV or other media, playing computer games and any similar screen activities (as main or secondary activity).
Americans use a computer for leisure for around 1.5 hours on an average weekday, most of that in the evening – 
Activity involvement and time spent on computers for leisure: an econometric analysis on the American Time Use Survey dataset.

That matters because your workspace hopefully includes some daylight.  But in the evening, you’re relying entirely on light from your screen and any other electric lights in the space. You’re also more likely to be working on a laptop or even on your mobile phone, increasing your risk of suffering from a cluster of painful symptoms known as ‘computer vision syndrome’ (or CVS) that affects around two in three adults worldwide- rising to up to a shocking 97% Pakistan – Prevalence of computer vision syndrome: a systematic review and meta-analysis.
 CVS not only reduces productivity, it’s linked to depression, headaches and quality of life overall – Computer Use, Symptoms, and Quality of Life.


So what can you do?   Here are five dimensions of visual fatigue and ways that lighting can help.

1. Accuracy. Insufficient light levels are directly linked to eye strain and stress. The latest standards for workplace lighting (EN 12464-1) recommends around 500 lux – Desktop lighting for comfortable use of a computer screenwhich should help to set your body clock too – Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adultsBut your need for light changes with age: a 60 year old has 36% less visual acuity than 30 year old –  WORKPLACE ILLUMINATION EFFECTS ON ACUITY, COGNITIVE PERFORMANCE AND WELL-BEING IN OLDER AND YOUNG PEOPLE.

2. Accommodation speed (how fast you can focus on objects at different distances in the room).

If your eyes spend hours on end fixed on a flat screen in front of you, the focus-flexing muscles get tired. Extreme contrast between the screen and the rest of the room will compound this ‘fixed focus’ problem as the pupil opens up or closes down to let in the optimal amount of light. All those muscles get stiff with age, so older people struggle more than their younger peers. Current research suggests the screen needs to be a bit brighter (1.3 to 1.7 times) than the rest of the room – a gentle glow.

Creating layers of light – adding fairy lights or a side lamp will encourage your eyes to ‘go for a walk’ and give them a gentle gradient of brightness.

3. Convergence – the ability of both eyes to work together to focus on an object and direct physical action, such as typing, using a mouse or a touch screen. This is closely linked to accommodation but relies on a different set of muscles and brain processing. Glare and distracting reflections on the screen disrupt this natural process. There is emerging evidence that a range of conditions including autism affect your ability to converge accurately and consistently, leading to increased risk of neck, shoulder and wrist pain.

Offering a large monitor on an adjustable arm, ergonomic keyboard, mouse and flexible task lighting will help to create optimal conditions for all.

4. Blink and blink rate: Blinking not only rinses and cleans the surface of your eye, it allows your brain to ‘buffer’ the information streaming along the optic nerve. Your blink rate falls from a natural average of 10 to 15 times per minute to around 5 to 7 times when looking at a screen, an effect that tends to get worse as the screen gets brighter.

This is another reason to create layers of light that balance the brightness of the screen and the rest of the room.

5. CFF: Critical Flicker Frequency (CFF) – Your ability to spot fast changes in light levels or movement. This fast light-dark cycle not only interrupts the natural movement of your eye across the scene, it triggers an alerting response in the central nervous system. This adds to fatigue and can lead to headaches or even epileptic fits –  Critical Flicker Fusion Frequency: Effect of Age, Gender, Sleep and Display Screens.

A screen with a high refresh rate is a good place to start. Poor-quality lights will also generate flicker, especially when dimmed to a low level. So my solution is to use a task light with a fixed light output and then simply move it to reduce the amount of light on the desk.


These are objective measures. But other contextual factors have a role to play too:

Personal control boosts visual comfort, eye-related symptoms, perceived task performance, pleasure, alertness and physiological arousal – Personal control of correlated color temperature of light: Effects on thermal comfort, visual comfort, and cognitive performance.

Simply believing that your workspace delivers good visual ergonomics is likely to boost your self-rated visual performance – Visually deficient working conditions and reduced work performance in office workers: Is it mediated by visual discomfort?

Interestingly, even if you believe your workplace is contributing to eyestrain, headaches, neck and back pain, you’re much less likely to complain if you feel supported, especially if you feel your supervisor listens to your concerns – The relationship among computer work, environmental design, and musculoskeletal and visual discomfort: examining the moderating role of supervisory relations and co-worker support


Priming and procrastination

My nieces are stressing about exams and struggle – like all of us to get down to boring or difficult tasks. 

Here are two ways you can help them to get in the mood using simple visual and lighting cues.

We take cues from other people about whether a task is hard or not. ‘Priming’, or setting expectations before a task can transform results as any coach or team leader knows. Seeing a sad face, even subliminally before caring out a task seems to make ir more effortful, as measured by cardiac response, compared to when we’re primed with a happy face –  Do sadness-primes make me work harder because they make me sad?

Another reason to choose a smiling screensaver and add a photo of happy times on your desk,

But simply feeling you have a choice about which task to do next seems to buffer against those negative effects, helping you to get on with the job The power of personal control: Task choice attenuates the effect of implicit sadness on sympathetically mediated cardiac response. 


How do you know how much light you’re getting when you’re sitting at your desk?  Being close to the window and looking out or facing away from it  and being far inside the room can make a big difference to your ability to stay focused and alert and even to sleep at night. 

So it’s really worth finding out

A professional light meter is obviously the way to go if you want consistent reliable scientifically proven results which includes all the wavelengths bouncing around inside the room. But if you really want just a very rough idea, a smartphone app can be a really great solution

Here are four different ones I tried out to see what you think

Lux is the simplest of all. It’s got a paid version with additional features, but mainly, just notice the way that the light levels shift as you change your gaze into the space. 

LEDvance is a manufacturer- sponsored version.

The numbers are different, but you see the same basic principles at work: 

As you shift our chair to look into the room the light levels fall away dramatically

LM-3000 is another one. It’s more precise, includes many more features in the paid version than the others and a similar range of values

Finally Photone, which consistently gets the best reviews for consistency and accuracy. It’s a very impressive piece of kit. The paid version includes a bunch of other features too.


Green – in the eye of the beholder?

Children learn colour categories in the first few years of life, slowly linking and fine-tuning the sensation of ‘green’ – or any other colour – with the words the adults around them use. The first few colour categories are the hardest for them to grasp as they first need to understand that colour is a quality that is independent of the object itself. 

Once those concepts are fixed (colour maturity), they will perceive a colour as broadly constant even under different lighting conditions. This is known as colour constancy (see the dress illusion – The dress).

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