LCD Display Discomfort
Although this article was written with great care, it may reflect personal opinions of the author, which are not necessarily shared by the publishers, who cannot assume any responsibility for mistakes or misprints. Nothing in this article should be regarded as medical advice. If you require medical or other expert assistance, you should consult a professional advisor.
As soon as I heard about LCD displays, and even more after seeing some flat panel monitors at computer shows, I became a fan of this technology. As a computer user sitting in front of a monitor for more hours than the sun shines in the sky, I was very happy that I would soon be able to enjoy a flicker-free and radiation-free alternative to bulky and power-hungry cathode ray tube monitors. That was until I tried them, beginning a story of hard to describe discomfort and an apparently vague relationship with existing research involving factors such as fluorescent light, flickering, lighting, glare, contrasts and patterns. I now refer to this as "LCD Syndrome".
If you reached this page because you are experiencing symptoms with a new monitor you may want to try and reduce the brightness and/or increase the general ambient lighting. Excessive display brightness and large contrast between the display and the environment are common and easily solvable causes of discomfort.
I found out in 1996 that I could not make full productive use of an LCD display (800x600 resolution) for longer than 20-30 minutes, after which I began to feel uncomfortable. This was not easy to describe, because the symptoms were not particularly strong, and they were going against the expectation and conventional wisdom that LCD displays were better than CRTs. I would say it was a combination of slight headache and eye irritation. I normally had no problems with fluorescent lighting, nor with any working environment in general. I do however feel a similar discomfort when standing for some time near certain mosquito killing devices which use a violet fluorescent tube to attract the insects.
A friend of mine develops symptoms similar to ones I experienced after only about 5 minutes, and he was the one who led me to the first apparent cause of this: the fluorescent light use for the backlighting of the display. He is a teacher, and the first thing he does when he enters a classroom is to switch off the fluorescent lights. He says he is "allergic" to fluorescent light. When he purchased a notebook with a black and white LCD display he found out that he had the same problem he has with fluorescent room lighting. I personally tried out a variety of LCD displays, from the cheap ones up to the high end, and I also spoke with a lot of people about this, concluding that the issue is surprisingly more widespread than I expected it to be. The feedback I am now receiving from this text also appears to confirm this.
Frankly, I was amazed and puzzled as to why none of the reviews of notebooks or LCD displays that I was aware of at the time had ever mentioned this. The first thing that came to my mind is that this is a relatively new technology, and the new parameters that need to be evaluated are not yet part of our testing and buying culture. A second aspect of this issue is that the problem in my experience only develops under real working conditions, rather than when admiring the sharp pixels of an LCD display for a few seconds at a trade show, or testing the LCD viewing angle for a review or in a computer store.
According to my personal observations with panels employing this technology, many people cannot work continuously with such a display for as long as they can with a traditional CRT. Some people feel a headache after about half an hour of work in front of an LCD panel, yet they can stay 16 hours in front of a CRT. My situation improved when I conducted tests on word processing tasks with white text on a black background, rather than black text on white background (which, traditionally, on a CRT with a sufficiently high refresh rate is considered to be more ergonomical).
I am not a doctor nor an expert in this field, and I did not have a chance to conduct tests on a sample wide enough to be considered significant. The feedback I am receiving may be biased, as it is increasingly based on this article (i.e. people may be finding a description of the problem they have been looking for, rather than an unexpected and new perspective). Yet I am left with this personal feeling that there is "something wrong" with LCD displays that has not been researched or mentioned enough. I hope that these notes of mine can inspire somebody to perform more thorough investigations.
While everybody appeared to be focused on the "zero radiation" advantage of LCD technology, I could not avoid thinking that, behind the liquid crystals (which the "L" and "C" letters stand for), there was a source of light. This happened to be the same fluorescent light technology which, I knew, was not recommended for use as the only light source in offices. So, if there was something less than ideal about using it too much in an office, how came nobody mentioned this in relation with the fact that LCD display users stare at such lights all day?
Checking things like the refresh rates and the frequency peaks of a source of fluorescent light is not normally done with CRT displays, and does not naturally cross one's mind when thinking of liquid crystal displays. The fluorescent light is a separate component from the LCD display, and is never mentioned as part of the final "LCD display" product.
Two aspects of fluorescent lighting are in my opinion worth mentioning.
As technology evolved over time, the average refresh frequency increased from less than 100 Hertz (times per second) to several hundreds or thousands of Hertz. With modern electronic ballast systems, frequencies above 20 kHz are generally chosen in order to avoid interference on frequencies that could be audible to the human ear. I know that many experts are claiming that we cannot perceive certain higher refresh rates, but when I consider that the sunlight does not go on and off all the time, but rather it is "always on", I can't avoid thinking that everything else is not as "natural", and the possible side effects may not be obvious.
The negative effects of 100% fluorescent room lighting have been known and studied for some time, and thinking about it from this perspective I would find it logical that directly staring at a source of fluorescent light can be just as bad, if not worse. I know that many people have problems with the energy-efficient fluorescent room illumination in general, and prefer the traditional light bulb, which I believe has a wider frequency spectrum.
The incandescent filament of a light bulb probably also generates a more stable light than the fluorescent substrate under the intermittent pulses of electrons. Assuming that fluorescent light is a bit like the scan lines of a television, i.e. it turns on and off all the time, but our eyes and nervous system make us perceive it as a persistent light, I cannot understand how some publications that praise LCD displays ignore this similarity with what is possibly the most negative aspect of CRT displays. Even if you don't normally perceive the flickering of your display or TV, if you point your eyes upwards, you may be able to discern some flickering in the lower part of the visual region (the peripheral area is more sensitive to flickering). I am sure that there is a range of frequencies, which may or may not include the refresh rates normally used for fluorescent light, which cannot be perceived by the average person, but which can cause discomfort in the longer term.
Even if it is claimed that flicker is not perceptible at rates of hundreds or thousands of times per second, it must also be considered that this applies to a single source of light, and not necessarily to multiple sources of lights, which may not be in sync with each other. In physics, when two or more waves are added up, they result in a new wave pattern. Interference phenomena might apply to LCD displays (e.g. displays that have two fluorescent tubes), room illumination (with multiple light sources), and combinations of LCD displays and room illumination.
Could it be that the fluorescent light is a factor or co-factor in this "LCD Syndrome"? And if so, is it because the spectral distribution of the light is not what evolution trained us to live with, or because a pulsating source of light is used for the background illumination, or for a combination of both reasons? I know people sensitive to fluorescent light, but also people sensitive to flickering in general (even to the way frames are displayed at movie theaters, which is considered relatively stable).
At the time of this writing, it is expected that LEDs and other technologies will replace fluorescent backlighting in LCD displays.
Other Causes of "Flickering"
Old fluorescent lights are not the only cause of flickering. Even when the most stable backlighting and content rendering technologies are available, fluctuations are sometimes added intentionally:
The above may result in additional interference patterns when combined with each other, and with room illumination or backlight.
Pixel Sharpness and Pixel Patterns
LCD displays are better known for their brightness and for their "sharp pixels" than for the fluorescent light they employ. What if one of those very same factors which are normally considered positive in benchmarks, such as its crisp pixels, were part of the problem?
On LCD displays the individual pixels are much sharper than on CRT displays, thereby making it possible for the eyes and the brain to:
I believe that both factors could introduce new potential causes of discomfort, compared to CRT technology, considering that neither with CRTs nor in real life do we normally have as many tiny details to focus on with such clarity, and for those parts of the brain which discern movement and high contrast images to work on.
Microsoft Windows includes a font smoothing technology called ClearType, which uses the colored sub-pixel components of LCD display pixels to increase the perceived resolution, while at the same time reducing the contrast and sharpness of the (larger) individual pixels. It can be enabled in the Appearance tab of the Display Properties, under Effects...
I later found out about research done in the field of "pattern glare", i.e. a hypersensitivity to repetitive patterns, including stripes and lines of print. It seems to correlate with my observations on pixel patterns, also considering that in my 1996 800x600 LCD monitor the individual pixels could be discerned much better than on newer monitors (which, at much higher resolutions, have significantly smaller pixels).
What else is so nice about LCD displays, besides their crisp pixels? Brightness, of course.
In my experience LCD displays have higher default brightness settings, and can reach an even higher level by adjusting the settings. A possible explanation for the high default settings may lie in a combination of technology and marketing. While CRT technology is limited in the maximum brightness that can be achieved (visible light is generated by the phosphor coating behind the glass when it is hit by an invisible beam of electrons), in LCD displays the rendering technology is separate from the light source, making it possible to use brighter sources of visible light. Since maximum brightness is often a parameter in monitor benchmarks, and it may help get noticed in a store, manufacturers are tempted to prefer (since it comes at a relatively low cost) high brightness technology in LCD displays.
One piece of advice I can give in case of perceived problems in relation to LCD displays is, indeed, to try and reduce (even drastically) the brightness settings, as these displays can be, in my personal experience, much brighter than CRTs. I have seen this solving more than one problem case. I set the brightness to 0 (!) on my Dell 2407WFP monitor, and it still doesn't look too dark even to bystanders. The ambient lighting should also not be too low, relative to the display. If you suffer from discomfort, try and adjust the environment so that the ambient-to-display brightness contrast is between 1:3 to 1:1 (room background and display are about the same perceived brightness).
Whereas sunlight and light emitted by incandescent bulbs and CRT displays oscillates in multiple directions perpendicular to the light beam, the fields from polarized light oscillate in only one direction. Polarized light is not only produced from certain light sources, but it can be the result of non-polarized light being reflected from certain surfaces (e.g. water or glass), or being filtered by polarized filters, which include certain sunglasses, liquid crystals, and the polarizer plastic sheets used in LCD displays. Several animals are able to detect light polarization. Some, like honeybees, use this sensitivity as an aid in their navigation.
On LCD displays a combination of polarized filters and the ability to electrically control the polarization angle of liquid crystal molecules is used to produce images. Two side effects of this technology are that:
Our sense of depth in viewing the real world is the result of several factors, which include the fact that each eye sees a slightly different view of the world. This is also used in stereoscopic (3D) visualization technologies, some of which have viewer discomfort as a well-known side effect. It is also known that when the angle or separation of two cameras used for a 3D film is not "natural", this may lead to headache. This may be caused by the inability to cope with excessive 3D cues, or by "wrong" cues altogether. If this is a factor affecting 3D display technologies, and considering that most LCD displays have a viewing angle limitation which results in slightly different images (colors) being received by each eye, there could in my opinion also be a relationship with LCD display discomfort.
Factors like the increased visibility of individual pixels and patterns of pixels (which phenomenon can be reduced, e.g. by using technologies such as ClearType or by using higher resolution displays), and the high brightness potential of LCD displays (which brightness can also easily be reduced by adjusting the monitor settings), lead to interesting parallels with the triggers and mechanisms which are related to headaches and other symptoms in a condition known as Scotopic Sensitivity Syndrome, Asfedia (Arrhythmic Saccade and Foveation During Edge Detection) or Meares-Irlen Syndrome.
When I first heard about companies like TintaVision and Irlen Institute I was prejudiced by the perception of organizations that seemed to be interested in selling colored glasses, filters and other "patented" methods without exposing a sound scientific method. I would have preferred some scientific research (published papers with double-blind studies and reproducible results, independently verified by others) rather than web sites providing only convenient examples and case studies going all in one direction. In the meantime, such research is beginning to appear. For example, see Bruce J. W. Evans and Florence Joseph in The effect of coloured filters on the rate of reading in an adult student population (Ophthalmic and Physiological Optics 2002 22: 535-545). At the same time, I could not find the topic being related by others to manifestations of LCD display discomfort. However, I also have observed how extreme brightness, which is on the opposite end of using colored lenses or reducing the monitor brightness, can be a factor in LCD discomfort.
Volatile organic compounds (VOCs) and other chemicals have been studied for years with respect to their relationship with "sick building syndrome" and discomfort related to "new car smell". The chemicals that can be released when new computer equipment is unboxed and used for the first few weeks are often similar to those that seep from walls, furniture, carpets, glues, paints and plastics in buildings and cars, and which have been linked to headaches, watery eyes, sore throats, nausea and drowsiness. The symptoms have been traced not only to the individual components, but also, in a larger measure, to their combination, and even more so when ozone (from laser printers, copiers or car traffic) is added.
If you bought a new display, and perhaps even a new computer, and you suspect this to be a factor, you may want to put the packaging away and pay extra attention to air quality in the first few weeks (up to six months, according to some studies relating to buildings and cars).
As of the end of 2001, i.e. after more than five years of additional experience since I first wrote this text, I keep getting a diversity of feedback from readers of this page, however I am now myself using the 1600x1200 pixel LCD display of my notebook computer (IBM ThinkPad A21p, pretty high resolution, I love it, but I know that other people are not at ease with the small pixels). I actually prefer the notebook display to the same resolution displayed by a top-of-the-line brand name 22" CRT set at a high refresh frequency. Although the LCD display is smaller, the pixels are much more detailed and crisper, resulting in the smaller display being much more readable than the larger one. This was, of course, also the case with the first LCD displays I tried more than five years ago, but something must have changed in the technology, or maybe it is the higher resolution, as I can now work all day on an LCD display without discomfort. It could be that at a resolution of 1600x1200 my eyes are not trying to focus on the individual pixels as they had possibly been doing at 800x600. Also, one of the first things I do on most new LCD displays is to reduce the brightness.
Changing the surrounding lighting (e.g. adding a small light to reduce the perceived brightness of the display) has also been reported to help. Quite often LCD displays are sharper, but smaller, than CRT displays having the same resolution, so that old habits may result in the LCD panel being positioned too far away, which also can cause a type of discomfort not experienced with larger displays. I've heard of cases where even an additional keyboard placed in front of a notebook computer caused the notebook (and its LCD display) to be placed too far away to be comfortable, yet the cause of the discomfort was not immediately obvious. On the other hand, the closer the distance the more likely it is that the eyes recognize the individual pixels, which may or may not be related to the perceived problem. Working with notebooks, where one can't easily adjust the distance and height of the display, we have moved one step back in ergonomics, compared to when independent keyboards where introduced (and often made compulsory with a lot of energy, compared to the silence that is accompanying the widespread use of notebooks).
It appears that LCD displays have introduced a new combination of elements which are not present in nature, possibly including issues such as spectral distribution, flickering, more recognizable pixels and patterns, increased brightness, polarization and "wrong" binocular cues. This is not what evolution has trained us to live with under the sun, and some people react to it differently than others. In particular, given a combination of these factors, some people appear to develop an "LCD Syndrome". I hope that this little research helps, at least to know that if you read this page up to this point, you are not alone.
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